diff --git a/CLAUDE.md b/CLAUDE.md
index 3b155ce..117607f 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -62,7 +62,7 @@ Location: `~/.config/terdut-tui/config.yaml`
 
 ```yaml
 server_url: https://terdut.example.com
-api_key: <64-char hex key>
+username: niklas      # optional, prefills the sign-in form
 refresh_interval: 30  # seconds, optional, default 30
 theme: gruvbox-dark   # optional, default gruvbox-dark
 team: Ops             # optional, team name or id to start on, default all
@@ -72,7 +72,14 @@ Built-in themes are `gruvbox-dark` and `gruvbox-light`; user themes are YAML
 files in `~/.config/terdut-tui/themes/`, optionally `extends:`-ing a built-in.
 See the README for the token list.
 
-The API key is a one-time secret generated by terdut-server (`POST /api/users/{id}/api-keys`).
+There is no API key in the config. The TUI signs in as a user (`POST /api/login`, the
+same session cookie as the web UI) and `internal/session` keeps the token in
+`~/.config/terdut-tui/session.json`, mode 0600, keyed by server URL. The client
+attaches `terdut_session` itself rather than using a cookie jar, because a jar drops the
+server's Secure cookie over plain http. It must never send `Authorization` as well: the
+server judges a request with that header on it alone. A 401 from anything (`msgError`
+in `update.go`) returns to the sign-in form and clears `Model`. A user with no password
+cannot sign in, and the server answers it like a wrong one, so the form says so.
 
 ## Running
 
@@ -105,6 +112,7 @@ go build -ldflags="-X main.version=v0.1.0" -o terdut-tui .
 | 5 | User management and API key lifecycle |
 | 6 | Incidents: queue, timeline, ack/assign/snooze/resolve, MTTA/MTTR |
 | 7 | Teams: `T` switcher, per-team schedule, admin/disabled markers (server v0.20) |
+| 8 | Sign in as a user instead of an API key (server v0.10+ session cookie) |
 
 <!-- graymatter:instructions:begin — managed by `graymatter init`; edits inside this block are overwritten -->
 ## Memory (GrayMatter)
diff --git a/README.md b/README.md
index 5519657..be61d8e 100644
--- a/README.md
+++ b/README.md
@@ -85,13 +85,31 @@ Create `~/.config/terdut-tui/config.yaml`:
 
 ```yaml
 server_url: https://terdut.example.com
-api_key: <your-api-key>
+username: niklas      # optional, prefills the sign-in form
 refresh_interval: 30  # seconds, optional
 theme: gruvbox-dark   # optional, this is the default
 team: Ops             # optional, a team name or id to start on; default is all
 ```
 
-The API key is generated in terdut-server. See the server documentation for how to bootstrap a user and issue an API key.
+## Signing in
+
+The TUI signs in the way the web UI does: with a user account's username and
+password, on a form shown at start. It keeps the server's session, not the
+password, in `~/.config/terdut-tui/session.json` (readable by you only), so the
+next start resumes it. The server's sessions last 30 days and slide with use.
+When it has ended, or the account is disabled or the session is ended from the web
+UI, the TUI returns to the form and says so. `L` signs out, which also ends the
+session on the server and deletes the saved one.
+
+The account needs a password, since that is what signing in uses. A user
+created only for API access has none and cannot sign in: the server answers it
+exactly like a wrong password. Set one in the web UI, or have an administrator
+press `p` on that user in Users. Too many failed attempts are rate limited by
+the server for a few minutes.
+
+> **Upgrading from v0.10.0 and earlier:** `api_key` in `config.yaml` is no longer
+> used. Remove it and sign in. API keys still exist on the server, and `k` in
+> Users still manages them, for whatever else uses them.
 
 ## Themes
 
@@ -152,6 +170,7 @@ Global:
 | `esc` | Go back |
 | `r` | Refresh |
 | `f` | Cycle filter |
+| `L` | Sign out |
 | `T` | Switch team: all → each of your teams (when you have more than one) |
 | `q` | Quit |
 
diff --git a/internal/api/client.go b/internal/api/client.go
index 4b2c64e..e9a4c3e 100644
--- a/internal/api/client.go
+++ b/internal/api/client.go
@@ -3,6 +3,7 @@ package api
 import (
 	"bytes"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"net/http"
 	"net/url"
@@ -11,29 +12,98 @@ import (
 	"time"
 )
 
+// SessionCookie is the cookie terdut-server's web UI signs in with.
+const SessionCookie = "terdut_session"
+
+// Client talks to terdut-server as the user who signed in. Login trades a
+// username and password for a session, the same one the web UI holds, and every
+// request after it carries that session's cookie.
+//
+// The cookie is attached by hand rather than through a cookie jar: the server
+// marks it Secure behind https, and a jar drops a Secure cookie it is handed
+// over plain http, which would make a local server unusable for no reason. There
+// is nothing else a jar would do here — the token is opaque and does not change
+// while the session lives.
 type Client struct {
 	baseURL    string
 	httpClient *http.Client
-	apiKey     string
+	session    string
 }
 
-func NewClient(baseURL, apiKey string) *Client {
+func NewClient(baseURL string) *Client {
 	return &Client{
 		baseURL: strings.TrimRight(baseURL, "/"),
-		apiKey:  apiKey,
 		httpClient: &http.Client{
 			Timeout: 10 * time.Second,
 		},
 	}
 }
 
+// SetSession resumes a session from a token saved earlier.
+func (c *Client) SetSession(token string) { c.session = token }
+
+// HasSession reports whether there is a session to try. It says nothing about
+// whether the server still honours it.
+func (c *Client) HasSession() bool { return c.session != "" }
+
+// Login signs in and returns the session token, which the client also keeps and
+// sends from then on. The server answers a wrong password, an unknown user and
+// an account with no password all with the same 401, so the caller cannot tell
+// them apart. Too many failures come back as 429.
+func (c *Client) Login(username, password string) (string, error) {
+	body := struct {
+		Username string `json:"username"`
+		Password string `json:"password"`
+	}{Username: username, Password: password}
+	req, err := c.newRequestWithBody(http.MethodPost, "/api/login", body)
+	if err != nil {
+		return "", err
+	}
+	// A stale session must not ride along on the request that replaces it.
+	req.Header.Del("Cookie")
+
+	resp, err := c.httpClient.Do(req)
+	if err != nil {
+		return "", err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode >= 400 {
+		return "", statusError(resp)
+	}
+	for _, ck := range resp.Cookies() {
+		if ck.Name == SessionCookie && ck.Value != "" {
+			c.session = ck.Value
+			return ck.Value, nil
+		}
+	}
+	return "", fmt.Errorf("server signed us in but sent no %s cookie", SessionCookie)
+}
+
+// Logout ends the session on the server and forgets it here.
+func (c *Client) Logout() error {
+	req, err := c.newRequest(http.MethodPost, "/api/logout")
+	if err != nil {
+		return err
+	}
+	err = c.do(req, nil)
+	c.session = ""
+	return err
+}
+
+// authorize puts the session on a request.
+func (c *Client) authorize(req *http.Request) {
+	req.Header.Set("Accept", "application/json")
+	if c.session != "" {
+		req.AddCookie(&http.Cookie{Name: SessionCookie, Value: c.session})
+	}
+}
+
 func (c *Client) newRequest(method, path string) (*http.Request, error) {
 	req, err := http.NewRequest(method, c.baseURL+path, nil)
 	if err != nil {
 		return nil, err
 	}
-	req.Header.Set("Authorization", "Bearer "+c.apiKey)
-	req.Header.Set("Accept", "application/json")
+	c.authorize(req)
 	return req, nil
 }
 
@@ -51,6 +121,21 @@ func (e *StatusError) Error() string {
 	return fmt.Sprintf("server returned %d", e.Code)
 }
 
+// IsUnauthorized reports whether err is the server refusing the session: it
+// expired, was ended elsewhere, or belongs to an account since disabled.
+func IsUnauthorized(err error) bool {
+	var se *StatusError
+	return errors.As(err, &se) && se.Code == http.StatusUnauthorized
+}
+
+func statusError(resp *http.Response) error {
+	var e struct {
+		Error string `json:"error"`
+	}
+	_ = json.NewDecoder(resp.Body).Decode(&e)
+	return &StatusError{Code: resp.StatusCode, Message: e.Error}
+}
+
 func (c *Client) do(req *http.Request, out any) error {
 	resp, err := c.httpClient.Do(req)
 	if err != nil {
@@ -59,11 +144,7 @@ func (c *Client) do(req *http.Request, out any) error {
 	defer resp.Body.Close()
 
 	if resp.StatusCode >= 400 {
-		var e struct {
-			Error string `json:"error"`
-		}
-		_ = json.NewDecoder(resp.Body).Decode(&e)
-		return &StatusError{Code: resp.StatusCode, Message: e.Error}
+		return statusError(resp)
 	}
 
 	if out != nil {
@@ -125,8 +206,7 @@ func (c *Client) newRequestWithBody(method, path string, body any) (*http.Reques
 	if err != nil {
 		return nil, err
 	}
-	req.Header.Set("Authorization", "Bearer "+c.apiKey)
-	req.Header.Set("Accept", "application/json")
+	c.authorize(req)
 	req.Header.Set("Content-Type", "application/json")
 	return req, nil
 }
diff --git a/internal/api/client_test.go b/internal/api/client_test.go
index d806f24..7877006 100644
--- a/internal/api/client_test.go
+++ b/internal/api/client_test.go
@@ -19,7 +19,9 @@ type call struct {
 	path   string
 	query  string
 	body   string
-	auth   string
+	cookie string
+	// authz is the Authorization header, which the client no longer sends at all.
+	authz string
 }
 
 // stub serves one canned response and records the request that fetched it.
@@ -29,22 +31,107 @@ func stub(t *testing.T, status int, response string) (*Client, *call) {
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		body, _ := io.ReadAll(r.Body)
 		got.method, got.path, got.query = r.Method, r.URL.Path, r.URL.RawQuery
-		got.body, got.auth = string(body), r.Header.Get("Authorization")
+		got.body, got.authz = string(body), r.Header.Get("Authorization")
+		if ck, err := r.Cookie(SessionCookie); err == nil {
+			got.cookie = ck.Value
+		}
 		w.Header().Set("Content-Type", "application/json")
 		w.WriteHeader(status)
 		io.WriteString(w, response)
 	}))
 	t.Cleanup(srv.Close)
-	return NewClient(srv.URL, "test-key"), got
+	c := NewClient(srv.URL)
+	c.SetSession("test-session")
+	return c, got
 }
 
-func TestClient_SendsBearerToken(t *testing.T) {
+func TestClient_SendsTheSessionCookie(t *testing.T) {
 	c, got := stub(t, http.StatusOK, `[]`)
 	if _, err := c.ListIncidents(0, "", false, false, 0); err != nil {
 		t.Fatalf("list: %v", err)
 	}
-	if got.auth != "Bearer test-key" {
-		t.Errorf("expected bearer token, got %q", got.auth)
+	if got.cookie != "test-session" {
+		t.Errorf("expected the session cookie, got %q", got.cookie)
+	}
+	// The server judges a request with an Authorization header on that alone and
+	// never falls back to the cookie, so sending one would defeat the session.
+	if got.authz != "" {
+		t.Errorf("expected no Authorization header, got %q", got.authz)
+	}
+}
+
+// Login has to work over plain http, where a cookie jar would discard the
+// Secure cookie a server behind https sets.
+func TestLogin_KeepsTheSessionFromTheCookie(t *testing.T) {
+	var body string
+	var sentCookie bool
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		b, _ := io.ReadAll(r.Body)
+		body = string(b)
+		_, err := r.Cookie(SessionCookie)
+		sentCookie = err == nil
+		http.SetCookie(w, &http.Cookie{Name: SessionCookie, Value: "fresh", Path: "/", HttpOnly: true, Secure: true})
+		w.WriteHeader(http.StatusOK)
+		io.WriteString(w, `{"user":{"id":1},"has_password":true}`)
+	}))
+	t.Cleanup(srv.Close)
+
+	c := NewClient(srv.URL)
+	c.SetSession("stale")
+	token, err := c.Login("niklas", "correct horse")
+	if err != nil {
+		t.Fatalf("login: %v", err)
+	}
+	if token != "fresh" || !c.HasSession() {
+		t.Errorf("expected the new token to be kept, got %q", token)
+	}
+	if body != `{"username":"niklas","password":"correct horse"}` {
+		t.Errorf("unexpected body %q", body)
+	}
+	if sentCookie {
+		t.Error("a stale session must not ride along on the login that replaces it")
+	}
+}
+
+func TestLogin_RefusalCarriesTheServersWords(t *testing.T) {
+	c, _ := stub(t, http.StatusUnauthorized, `{"error":"invalid username or password"}`)
+	_, err := c.Login("niklas", "wrong")
+	if !IsUnauthorized(err) || !strings.Contains(err.Error(), "invalid username or password") {
+		t.Errorf("expected the server's 401 message, got %v", err)
+	}
+
+	c, _ = stub(t, http.StatusTooManyRequests, `{"error":"too many attempts"}`)
+	if _, err := c.Login("niklas", "wrong"); err == nil || IsUnauthorized(err) {
+		t.Errorf("a rate limit is not an authentication failure, got %v", err)
+	}
+}
+
+func TestLogin_NoCookieIsAnError(t *testing.T) {
+	c, _ := stub(t, http.StatusOK, `{}`)
+	if _, err := c.Login("niklas", "pw"); err == nil {
+		t.Error("a 200 without a session cookie is not a sign-in")
+	}
+}
+
+func TestLogout_ForgetsTheSession(t *testing.T) {
+	c, got := stub(t, http.StatusNoContent, ``)
+	if err := c.Logout(); err != nil {
+		t.Fatalf("logout: %v", err)
+	}
+	if got.method != "POST" || got.path != "/api/logout" || got.cookie != "test-session" {
+		t.Errorf("unexpected request %s %s cookie=%q", got.method, got.path, got.cookie)
+	}
+	if c.HasSession() {
+		t.Error("the session should be gone locally")
+	}
+}
+
+func TestIsUnauthorized(t *testing.T) {
+	if !IsUnauthorized(&StatusError{Code: 401}) {
+		t.Error("a 401 is unauthorized")
+	}
+	if IsUnauthorized(&StatusError{Code: 403}) || IsUnauthorized(errors.New("x")) || IsUnauthorized(nil) {
+		t.Error("only a 401 means the session is refused; a 403 is a permission")
 	}
 }
 
diff --git a/internal/config/config.go b/internal/config/config.go
index 58d22e1..2615fa0 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -13,10 +13,14 @@ const defaultRefreshInterval = 30 * time.Second
 
 type Config struct {
 	ServerURL       string
-	APIKey          string
+	Username        string // optional, prefills the sign-in form
 	RefreshInterval time.Duration
 	Theme           string
 
+	// LegacyAPIKey is set when the file still has an `api_key`. The TUI signs in
+	// with a user account now and ignores it; this is only so it can say so.
+	LegacyAPIKey bool
+
 	// Team is the team to start on, by name or id. Empty shows every team the
 	// key's user belongs to.
 	Team string
@@ -24,7 +28,8 @@ type Config struct {
 
 type rawConfig struct {
 	ServerURL       string `yaml:"server_url"`
-	APIKey          string `yaml:"api_key"`
+	Username        string `yaml:"username,omitempty"`
+	APIKey          string `yaml:"api_key,omitempty"`          // no longer used; see Config.LegacyAPIKey
 	RefreshInterval int    `yaml:"refresh_interval,omitempty"` // seconds
 	Theme           string `yaml:"theme,omitempty"`
 	Team            string `yaml:"team,omitempty"`
@@ -40,7 +45,7 @@ func Load() (*Config, error) {
 	data, err := os.ReadFile(path)
 	if err != nil {
 		if os.IsNotExist(err) {
-			return nil, fmt.Errorf("config file not found at %s\n\nCreate it with:\n  server_url: https://terdut.example.com\n  api_key: <your-api-key>\n  theme: gruvbox-dark  # optional\n  team: Ops            # optional, team to start on", path)
+			return nil, fmt.Errorf("config file not found at %s\n\nCreate it with:\n  server_url: https://terdut.example.com\n  username: <your-username>  # optional, prefills the sign-in form\n  theme: gruvbox-dark  # optional\n  team: Ops            # optional, team to start on", path)
 		}
 		return nil, fmt.Errorf("cannot read config file: %w", err)
 	}
@@ -53,9 +58,6 @@ func Load() (*Config, error) {
 	if raw.ServerURL == "" {
 		return nil, fmt.Errorf("config: 'server_url' is required")
 	}
-	if raw.APIKey == "" {
-		return nil, fmt.Errorf("config: 'api_key' is required")
-	}
 
 	interval := defaultRefreshInterval
 	if raw.RefreshInterval > 0 {
@@ -64,7 +66,8 @@ func Load() (*Config, error) {
 
 	return &Config{
 		ServerURL:       raw.ServerURL,
-		APIKey:          raw.APIKey,
+		Username:        raw.Username,
+		LegacyAPIKey:    raw.APIKey != "",
 		RefreshInterval: interval,
 		Theme:           raw.Theme,
 		Team:            raw.Team,
diff --git a/internal/config/config_test.go b/internal/config/config_test.go
index aa618e4..56cbc54 100644
--- a/internal/config/config_test.go
+++ b/internal/config/config_test.go
@@ -19,7 +19,7 @@ func writeConfig(t *testing.T, body string) {
 }
 
 func TestLoad_TeamIsOptional(t *testing.T) {
-	writeConfig(t, "server_url: https://terdut.example.com\napi_key: k\n")
+	writeConfig(t, "server_url: https://terdut.example.com\n")
 	cfg, err := Load()
 	if err != nil {
 		t.Fatalf("load: %v", err)
@@ -28,7 +28,7 @@ func TestLoad_TeamIsOptional(t *testing.T) {
 		t.Errorf("expected no default team, got %q", cfg.Team)
 	}
 
-	writeConfig(t, "server_url: https://terdut.example.com\napi_key: k\nteam: Ops\n")
+	writeConfig(t, "server_url: https://terdut.example.com\nteam: Ops\n")
 	cfg, err = Load()
 	if err != nil {
 		t.Fatalf("load: %v", err)
@@ -37,3 +37,25 @@ func TestLoad_TeamIsOptional(t *testing.T) {
 		t.Errorf("expected team Ops, got %q", cfg.Team)
 	}
 }
+
+// Signing in replaced the API key, so a config that has only a server URL is
+// complete, and one that still carries an api_key is noted rather than refused.
+func TestLoad_NoAPIKeyNeeded(t *testing.T) {
+	writeConfig(t, "server_url: https://terdut.example.com\nusername: niklas\n")
+	cfg, err := Load()
+	if err != nil {
+		t.Fatalf("load: %v", err)
+	}
+	if cfg.Username != "niklas" || cfg.LegacyAPIKey {
+		t.Errorf("unexpected config %+v", cfg)
+	}
+
+	writeConfig(t, "server_url: https://terdut.example.com\napi_key: old\n")
+	cfg, err = Load()
+	if err != nil {
+		t.Fatalf("a leftover api_key must not stop the TUI starting: %v", err)
+	}
+	if !cfg.LegacyAPIKey {
+		t.Error("expected the leftover api_key to be noted")
+	}
+}
diff --git a/internal/session/session.go b/internal/session/session.go
new file mode 100644
index 0000000..b3a8de6
--- /dev/null
+++ b/internal/session/session.go
@@ -0,0 +1,98 @@
+// Package session keeps the signed-in session between runs, so the TUI does not
+// ask for a password every time it starts.
+//
+// What is stored is the server's session token, not the password: it is what the
+// web UI keeps in a cookie, it expires on the server's schedule (30 days, sliding
+// with use) and signing out or a password change ends it. It is still a
+// credential, so the file is readable by its owner only.
+package session
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+type file struct {
+	ServerURL string `json:"server_url"`
+	Token     string `json:"token"`
+}
+
+func path() (string, error) {
+	dir, err := os.UserConfigDir()
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(dir, "terdut-tui", "session.json"), nil
+}
+
+// normalise makes two spellings of one server compare equal.
+func normalise(serverURL string) string {
+	return strings.TrimRight(serverURL, "/")
+}
+
+// Load returns the saved token for serverURL, or "" when there is none. A session
+// saved for a different server is not offered to this one, and an unreadable file
+// is the same as no file: the worst outcome is being asked to sign in.
+func Load(serverURL string) string {
+	p, err := path()
+	if err != nil {
+		return ""
+	}
+	data, err := os.ReadFile(p)
+	if err != nil {
+		return ""
+	}
+	var f file
+	if json.Unmarshal(data, &f) != nil || normalise(f.ServerURL) != normalise(serverURL) {
+		return ""
+	}
+	return f.Token
+}
+
+// Save stores the token for serverURL, replacing whatever was there.
+func Save(serverURL, token string) error {
+	p, err := path()
+	if err != nil {
+		return err
+	}
+	if err := os.MkdirAll(filepath.Dir(p), 0o700); err != nil {
+		return err
+	}
+	data, err := json.Marshal(file{ServerURL: normalise(serverURL), Token: token})
+	if err != nil {
+		return err
+	}
+	// Written beside the target and renamed over it, so a crash cannot leave a
+	// half-written token, and created 0600 so it is never briefly world-readable.
+	tmp, err := os.CreateTemp(filepath.Dir(p), ".session-*")
+	if err != nil {
+		return err
+	}
+	defer os.Remove(tmp.Name())
+	if err := os.Chmod(tmp.Name(), 0o600); err != nil {
+		tmp.Close()
+		return err
+	}
+	if _, err := tmp.Write(data); err != nil {
+		tmp.Close()
+		return err
+	}
+	if err := tmp.Close(); err != nil {
+		return err
+	}
+	return os.Rename(tmp.Name(), p)
+}
+
+// Clear forgets the saved session. Having none to forget is not an error.
+func Clear() error {
+	p, err := path()
+	if err != nil {
+		return err
+	}
+	if err := os.Remove(p); err != nil && !os.IsNotExist(err) {
+		return err
+	}
+	return nil
+}
diff --git a/internal/session/session_test.go b/internal/session/session_test.go
new file mode 100644
index 0000000..df82152
--- /dev/null
+++ b/internal/session/session_test.go
@@ -0,0 +1,92 @@
+package session
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func isolate(t *testing.T) {
+	t.Helper()
+	t.Setenv("XDG_CONFIG_HOME", t.TempDir())
+}
+
+func TestSaveThenLoad(t *testing.T) {
+	isolate(t)
+	if got := Load("https://terdut.example.com"); got != "" {
+		t.Fatalf("expected no session yet, got %q", got)
+	}
+	if err := Save("https://terdut.example.com", "tok"); err != nil {
+		t.Fatalf("save: %v", err)
+	}
+	if got := Load("https://terdut.example.com"); got != "tok" {
+		t.Errorf("expected tok, got %q", got)
+	}
+	// A trailing slash is the same server.
+	if got := Load("https://terdut.example.com/"); got != "tok" {
+		t.Errorf("a trailing slash should not lose the session, got %q", got)
+	}
+}
+
+// A token is only ever valid for the server that issued it; offering it to a
+// different one would send a credential to somebody it was never meant for.
+func TestLoadIgnoresAnotherServersSession(t *testing.T) {
+	isolate(t)
+	if err := Save("https://a.example.com", "tok"); err != nil {
+		t.Fatal(err)
+	}
+	if got := Load("https://b.example.com"); got != "" {
+		t.Errorf("a session for another server must not be reused, got %q", got)
+	}
+}
+
+func TestSaveIsOwnerOnly(t *testing.T) {
+	isolate(t)
+	if err := Save("https://a.example.com", "tok"); err != nil {
+		t.Fatal(err)
+	}
+	p, _ := path()
+	info, err := os.Stat(p)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if perm := info.Mode().Perm(); perm != 0o600 {
+		t.Errorf("the session file holds a credential and must be 0600, got %o", perm)
+	}
+	entries, _ := os.ReadDir(filepath.Dir(p))
+	for _, e := range entries {
+		if e.Name() != "session.json" {
+			t.Errorf("a temporary file was left behind: %s", e.Name())
+		}
+	}
+}
+
+func TestClear(t *testing.T) {
+	isolate(t)
+	if err := Clear(); err != nil {
+		t.Errorf("clearing nothing is not an error, got %v", err)
+	}
+	if err := Save("https://a.example.com", "tok"); err != nil {
+		t.Fatal(err)
+	}
+	if err := Clear(); err != nil {
+		t.Fatalf("clear: %v", err)
+	}
+	if got := Load("https://a.example.com"); got != "" {
+		t.Errorf("expected the session gone, got %q", got)
+	}
+}
+
+func TestLoadToleratesGarbage(t *testing.T) {
+	isolate(t)
+	p, _ := path()
+	if err := os.MkdirAll(filepath.Dir(p), 0o700); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(p, []byte("{not json"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if got := Load("https://a.example.com"); got != "" {
+		t.Errorf("an unreadable file means no session, got %q", got)
+	}
+}
diff --git a/internal/tui/login_test.go b/internal/tui/login_test.go
new file mode 100644
index 0000000..1bebc69
--- /dev/null
+++ b/internal/tui/login_test.go
@@ -0,0 +1,242 @@
+package tui
+
+import (
+	"errors"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+	"time"
+
+	"git.ryuvia.com/niklas/terdut-tui/internal/api"
+	"git.ryuvia.com/niklas/terdut-tui/internal/session"
+	"git.ryuvia.com/niklas/terdut-tui/internal/theme"
+	tea "github.com/charmbracelet/bubbletea"
+)
+
+// signedOut is a model with no session, so it starts on the sign-in form.
+func signedOut(serverURL string) Model {
+	m := NewModel(api.NewClient(serverURL), serverURL, time.Minute, theme.GruvboxDark)
+	m.width, m.height = 120, 40
+	return m
+}
+
+func TestStartsOnTheFormWithoutASession(t *testing.T) {
+	m := signedOut("http://test")
+	if m.mode != modeLogin {
+		t.Fatalf("expected the sign-in form, got mode %v", m.mode)
+	}
+	if m.Init() != nil {
+		t.Error("with no session there is nothing to connect with yet")
+	}
+}
+
+func TestStartsConnectedWithASavedSession(t *testing.T) {
+	c := api.NewClient("http://test")
+	c.SetSession("saved")
+	m := NewModel(c, "http://test", time.Minute, theme.GruvboxDark)
+	if m.mode == modeLogin {
+		t.Fatal("a saved session should be tried before asking for a password")
+	}
+	if m.Init() == nil {
+		t.Error("expected the saved session to be tried on start")
+	}
+}
+
+func TestLoginForm_ChecksBothFieldsBeforeSending(t *testing.T) {
+	m := signedOut("http://test")
+	m, cmd := press(t, m, "enter")
+	if cmd != nil || m.loggingIn || !strings.Contains(m.loginErr, "username") {
+		t.Errorf("an empty form must not be sent, got err %q", m.loginErr)
+	}
+
+	m = typeInto(t, m, "niklas")
+	m, cmd = press(t, m, "enter")
+	if cmd != nil || m.loggingIn || !strings.Contains(m.loginErr, "password") {
+		t.Errorf("a missing password must not be sent, got err %q", m.loginErr)
+	}
+}
+
+func TestLoginForm_QIsTypedNotQuit(t *testing.T) {
+	m := signedOut("http://test")
+	m = typeInto(t, m, "quentin")
+	if got := m.loginInputs[loginUsername].Value(); got != "quentin" {
+		t.Errorf("q is a letter in a username, got %q", got)
+	}
+}
+
+// The whole flow against a server: type both fields, submit, and the session is
+// kept for the next run.
+func TestLogin_SignsInAndSavesTheSession(t *testing.T) {
+	t.Setenv("XDG_CONFIG_HOME", t.TempDir())
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		b, _ := io.ReadAll(r.Body)
+		if r.URL.Path != "/api/login" || string(b) != `{"username":"niklas","password":"secret-pass"}` {
+			t.Errorf("unexpected request %s %s", r.URL.Path, b)
+		}
+		http.SetCookie(w, &http.Cookie{Name: api.SessionCookie, Value: "tok-1", Path: "/"})
+		io.WriteString(w, `{}`)
+	}))
+	t.Cleanup(srv.Close)
+
+	m := signedOut(srv.URL)
+	m = typeInto(t, m, "niklas")
+	m, _ = press(t, m, "tab")
+	m = typeInto(t, m, "secret-pass")
+	m, cmd := press(t, m, "enter")
+	if !m.loggingIn || cmd == nil {
+		t.Fatal("expected the sign-in to be under way")
+	}
+
+	msg := cmd()
+	if _, ok := msg.(loginDoneMsg); !ok {
+		t.Fatalf("expected loginDoneMsg, got %#v", msg)
+	}
+	if got := session.Load(srv.URL); got != "tok-1" {
+		t.Errorf("expected the session saved for next time, got %q", got)
+	}
+
+	next, connect := m.Update(msg)
+	m = next.(Model)
+	if m.mode != modeDashboard || m.loggingIn || connect == nil {
+		t.Errorf("expected to move on and connect, got mode %v", m.mode)
+	}
+	if m.loginInputs[loginPassword].Value() != "" {
+		t.Error("the password must not be kept once it has been used")
+	}
+}
+
+func TestLogin_WrongPasswordStaysOnTheForm(t *testing.T) {
+	m := signedOut("http://test")
+	m.loggingIn = true
+	next, _ := m.Update(loginErrMsg{&api.StatusError{Code: 401, Message: "invalid username or password"}})
+	m = next.(Model)
+	if m.mode != modeLogin || m.loggingIn {
+		t.Fatalf("expected to be back on the form, got mode %v", m.mode)
+	}
+	// The server gives the same 401 for an account with no password, so the
+	// message has to say so or it reads as a typo.
+	if !strings.Contains(m.loginErr, "no password") {
+		t.Errorf("expected the no-password hint, got %q", m.loginErr)
+	}
+	if m.loginFocus != loginPassword {
+		t.Error("focus should return to the password to retry")
+	}
+
+	next, _ = m.Update(loginErrMsg{&api.StatusError{Code: 429, Message: "slow down"}})
+	if got := next.(Model).loginErr; !strings.Contains(got, "too many") {
+		t.Errorf("expected the rate limit explained, got %q", got)
+	}
+	next, _ = m.Update(loginErrMsg{errors.New("dial tcp: refused")})
+	if got := next.(Model).loginErr; !strings.Contains(got, "refused") {
+		t.Errorf("other errors should show as they are, got %q", got)
+	}
+}
+
+// A 401 anywhere means the session is gone. Every action would fail the same
+// way, so it goes back to the form instead, without keeping the old data.
+func TestUnauthorized_ReturnsToTheFormAndDropsTheData(t *testing.T) {
+	for name, msg := range map[string]tea.Msg{
+		"refresh":  fetchDataErrMsg{&api.StatusError{Code: 401}},
+		"action":   actionErrMsg{&api.StatusError{Code: 401}},
+		"schedule": scheduleActionErrMsg{&api.StatusError{Code: 401}},
+		"connect":  connectErrMsg{&api.StatusError{Code: 401}},
+	} {
+		t.Run(name, func(t *testing.T) {
+			m := sized()
+			m.incidents = []api.Incident{{ID: 1, Title: "secret incident"}}
+			m.teams = twoTeams()
+			m.isAdmin = true
+			m.loginInputs[loginUsername].SetValue("niklas")
+
+			next, cmd := m.Update(msg)
+			m = next.(Model)
+			if m.mode != modeLogin || m.connected {
+				t.Fatalf("expected the sign-in form, got mode %v connected=%v", m.mode, m.connected)
+			}
+			if len(m.incidents) != 0 || len(m.teams) != 0 || m.isAdmin {
+				t.Error("the previous session's data must not survive into the next sign-in")
+			}
+			if cmd == nil {
+				t.Error("the dead session should be forgotten on disk")
+			}
+			if !strings.Contains(m.loginNote, "session") {
+				t.Errorf("expected the reason, got %q", m.loginNote)
+			}
+			if m.loginInputs[loginUsername].Value() != "niklas" || m.loginFocus != loginPassword {
+				t.Error("the username should be kept so only the password is retyped")
+			}
+			if strings.Contains(m.View(), "secret incident") {
+				t.Error("nothing from the old session may still be on screen")
+			}
+		})
+	}
+}
+
+// A 403 is a permission, not a lost session: it must not sign anybody out.
+func TestForbidden_DoesNotSignOut(t *testing.T) {
+	m := sized()
+	next, _ := m.Update(actionErrMsg{&api.StatusError{Code: 403, Message: "administrator access required"}})
+	if got := next.(Model); got.mode == modeLogin || !got.connected {
+		t.Error("a 403 must leave the session alone")
+	}
+}
+
+func TestLogout(t *testing.T) {
+	t.Setenv("XDG_CONFIG_HOME", t.TempDir())
+	m := sized()
+	m.teams = twoTeams()
+	m.incidents = []api.Incident{{ID: 1}}
+	m, cmd := press(t, m, "L")
+	if cmd == nil {
+		t.Fatal("L should sign out")
+	}
+	next, _ := m.Update(logoutDoneMsg{})
+	m = next.(Model)
+	if m.mode != modeLogin || m.connected || len(m.incidents) != 0 {
+		t.Errorf("expected the form with nothing loaded, got mode %v", m.mode)
+	}
+	if !strings.Contains(m.loginNote, "signed out") {
+		t.Errorf("expected it to say so, got %q", m.loginNote)
+	}
+}
+
+// Signing out and in again must not leave two refresh timers running, each
+// re-arming itself for ever.
+func TestSigningInAgainStartsNoSecondTimer(t *testing.T) {
+	m := sized()
+	next, _ := m.Update(connectedMsg{})
+	m = next.(Model)
+	if !m.ticking {
+		t.Fatal("the first connect starts the refresh timer")
+	}
+	m = m.requireLogin("x")
+	if !m.ticking {
+		t.Fatal("the timer is still running while signed out")
+	}
+	// Ticks while signed out must do nothing rather than fetch.
+	if _, cmd := m.Update(tickMsg(time.Now())); cmd == nil {
+		t.Error("the timer keeps ticking")
+	}
+	if cmd := m.refreshActiveSection(); cmd != nil {
+		t.Error("no refresh should be attempted while signed out")
+	}
+}
+
+func TestLoginView_HidesThePasswordAndShowsTheNote(t *testing.T) {
+	m := signedOut("https://terdut.example.com").WithLogin("niklas", "api_key in config.yaml is no longer used")
+	if m.loginFocus != loginPassword {
+		t.Error("with the username known the cursor should start on the password")
+	}
+	m = typeInto(t, m, "hunter2-hunter2")
+	view := m.View()
+	for _, want := range []string{"Sign in to https://terdut.example.com", "niklas", "api_key in config.yaml is no longer used"} {
+		if !strings.Contains(view, want) {
+			t.Errorf("expected %q on the form:\n%s", want, view)
+		}
+	}
+	if strings.Contains(view, "hunter2") {
+		t.Error("the password must be masked")
+	}
+}
diff --git a/internal/tui/model.go b/internal/tui/model.go
index 2674636..fd8523c 100644
--- a/internal/tui/model.go
+++ b/internal/tui/model.go
@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"git.ryuvia.com/niklas/terdut-tui/internal/api"
+	"git.ryuvia.com/niklas/terdut-tui/internal/session"
 	"git.ryuvia.com/niklas/terdut-tui/internal/theme"
 	"github.com/charmbracelet/bubbles/help"
 	"github.com/charmbracelet/bubbles/key"
@@ -52,6 +53,14 @@ const (
 	modeAPIKeyReveal
 	modeAPIKeyRevokeByID
 	modePasswordSet
+	modeLogin
+)
+
+// Fields of the sign-in form, in tab order.
+const (
+	loginUsername = iota
+	loginPassword
+	loginFieldCount
 )
 
 // Fields of the set-password form, in tab order.
@@ -115,6 +124,9 @@ type connectedMsg struct {
 	me    api.Me
 }
 type connectErrMsg struct{ err error }
+type loginDoneMsg struct{}
+type loginErrMsg struct{ err error }
+type logoutDoneMsg struct{}
 type incidentsFetchedMsg struct{ incidents []api.Incident }
 type archivedIncidentsFetchedMsg struct{ incidents []api.Incident }
 type incidentActionDoneMsg struct {
@@ -188,6 +200,7 @@ type Model struct {
 	client          *api.Client
 	serverURL       string
 	refreshInterval time.Duration
+	theme           theme.Theme // kept to build a fresh model when signing out
 
 	activeSection section
 	mode          mode
@@ -203,6 +216,17 @@ type Model struct {
 	meID         int64
 	isAdmin      bool
 
+	// Sign-in. Until the server accepts a session the TUI is in modeLogin;
+	// loginNote is a line the form shows above the fields (why we are here), and
+	// ticking says the refresh timer is already running, so signing in again
+	// after signing out does not start a second one.
+	loginInputs [loginFieldCount]textinput.Model
+	loginFocus  int
+	loggingIn   bool
+	loginErr    string
+	loginNote   string
+	ticking     bool
+
 	// Connection & dashboard
 	connected     bool
 	loading       bool
@@ -365,6 +389,18 @@ func NewModel(client *api.Client, serverURL string, refreshInterval time.Duratio
 		pwIn[i].CharLimit = 72 // bcrypt's limit; the server refuses longer
 	}
 
+	var loginIn [loginFieldCount]textinput.Model
+	for i, placeholder := range [loginFieldCount]string{"username", "password"} {
+		loginIn[i] = textinput.New()
+		loginIn[i].Placeholder = placeholder
+		loginIn[i].CharLimit = 72 // bcrypt's limit, and the server refuses longer passwords
+	}
+	loginIn[loginPassword].EchoMode = textinput.EchoPassword
+	loginIn[loginPassword].EchoCharacter = '•'
+	for i := range loginIn {
+		loginIn[i] = st.Input(loginIn[i])
+	}
+
 	for _, in := range []*textinput.Model{
 		&noteIn, &snoozeIn, &usernameIn, &emailIn, &topicIn, &keyNameIn, &revokeIn,
 	} {
@@ -385,12 +421,20 @@ func NewModel(client *api.Client, serverURL string, refreshInterval time.Duratio
 	}
 	window := today.AddDate(0, 0, -(weekday - 1))
 
+	startMode := modeDashboard
+	if client != nil && !client.HasSession() {
+		startMode = modeLogin
+		loginIn[loginUsername].Focus()
+	}
+
 	return Model{
 		client:            client,
 		serverURL:         serverURL,
 		refreshInterval:   refreshInterval,
+		theme:             th,
 		activeSection:     sectionIncidents,
-		mode:              modeDashboard,
+		mode:              startMode,
+		loginInputs:       loginIn,
 		loading:           true,
 		incidentFilter:    "",
 		alertFilter:       "firing",
@@ -424,7 +468,25 @@ func (m Model) WithDefaultTeam(team string) Model {
 	return m
 }
 
+// WithLogin prefills the sign-in form's username and sets a note shown above it.
+func (m Model) WithLogin(username, note string) Model {
+	m.loginInputs[loginUsername].SetValue(username)
+	m.loginNote = note
+	if username != "" && m.mode == modeLogin {
+		// The name is known, so the only thing left to type is the password.
+		m.loginInputs[loginUsername].Blur()
+		m.loginFocus = loginPassword
+		m.loginInputs[loginPassword].Focus()
+	}
+	return m
+}
+
+// Init tries the saved session, if there is one; otherwise the sign-in form is
+// already showing and there is nothing to do until it is submitted.
 func (m Model) Init() tea.Cmd {
+	if m.mode == modeLogin {
+		return nil
+	}
 	return connectCmd(m.client)
 }
 
@@ -975,6 +1037,38 @@ func connectCmd(client *api.Client) tea.Cmd {
 	}
 }
 
+// loginCmd signs in and saves the session, so the next run can resume it. Failing
+// to save is not failing to sign in: the session works for this run either way.
+func loginCmd(client *api.Client, serverURL, username, password string) tea.Cmd {
+	return func() tea.Msg {
+		token, err := client.Login(username, password)
+		if err != nil {
+			return loginErrMsg{err}
+		}
+		_ = session.Save(serverURL, token)
+		return loginDoneMsg{}
+	}
+}
+
+// logoutCmd ends the session on the server and deletes the saved one. The saved
+// copy goes even when the server cannot be reached, because the person asked to
+// be signed out and a token left on disk would say otherwise.
+func logoutCmd(client *api.Client) tea.Cmd {
+	return func() tea.Msg {
+		_ = client.Logout()
+		_ = session.Clear()
+		return logoutDoneMsg{}
+	}
+}
+
+// forgetSessionCmd drops a saved session the server no longer honours.
+func forgetSessionCmd() tea.Cmd {
+	return func() tea.Msg {
+		_ = session.Clear()
+		return nil
+	}
+}
+
 func fetchIncidentsCmd(client *api.Client, teamID int64, filter string) tea.Cmd {
 	return func() tea.Msg {
 		status, snoozed := incidentQuery(filter)
diff --git a/internal/tui/update.go b/internal/tui/update.go
index 59b9c4d..ea22f0f 100644
--- a/internal/tui/update.go
+++ b/internal/tui/update.go
@@ -1,7 +1,9 @@
 package tui
 
 import (
+	"errors"
 	"fmt"
+	"net/http"
 	"slices"
 	"strconv"
 	"strings"
@@ -13,6 +15,14 @@ import (
 )
 
 func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
+	// A 401 from anything means the server no longer honours the session: it
+	// expired, was ended from the web UI, or the account was disabled. Whatever
+	// was being done cannot succeed, so go back to the sign-in form and say why,
+	// rather than leaving every action to fail with "server returned 401".
+	if err := msgError(msg); api.IsUnauthorized(err) && m.mode != modeLogin {
+		return m.requireLogin("your session has ended — sign in again"), forgetSessionCmd()
+	}
+
 	switch msg := msg.(type) {
 	case tea.WindowSizeMsg:
 		m.width = msg.Width
@@ -33,6 +43,26 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 
 	// ── Dashboard messages ────────────────────────────────────────────────
 
+	case loginDoneMsg:
+		m.loggingIn = false
+		m.loginErr = ""
+		m.loginNote = ""
+		m.loginInputs[loginPassword].Reset()
+		m.blurLoginForm()
+		m.mode = modeDashboard
+		m.err = nil
+		return m, connectCmd(m.client)
+
+	case loginErrMsg:
+		m.loggingIn = false
+		m.loginErr = loginErrorText(msg.err)
+		m.loginInputs[loginPassword].Reset()
+		m.focusLogin(loginPassword)
+		return m, nil
+
+	case logoutDoneMsg:
+		return m.requireLogin("you have signed out"), nil
+
 	case connectedMsg:
 		firstConnect := len(m.teams) == 0
 		m.connected = true
@@ -52,8 +82,13 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 		m.rebuildIncidentTable()
 		m.rebuildTable()
 		m.rebuildArchivedTable()
+		var tick tea.Cmd
+		if !m.ticking {
+			m.ticking = true
+			tick = tickCmd(m.refreshInterval)
+		}
 		return m, tea.Batch(
-			tickCmd(m.refreshInterval),
+			tick,
 			fetchIncidentsCmd(m.client, m.activeTeamID, m.incidentFilter),
 			fetchStatsCmd(m.client),
 			statusCmd,
@@ -338,6 +373,14 @@ func (m Model) routeKey(msg tea.KeyMsg) (Model, tea.Cmd) {
 	case modeAPIKeyMenu, modeAPIKeyReveal:
 		return m.handleKey(msg)
 
+	case modeLogin:
+		var inputCmd tea.Cmd
+		if !m.loggingIn {
+			m.loginInputs[m.loginFocus], inputCmd = m.loginInputs[m.loginFocus].Update(msg)
+		}
+		m2, ourCmd := m.handleKey(msg)
+		return m2, tea.Batch(inputCmd, ourCmd)
+
 	case modePasswordSet:
 		var inputCmd tea.Cmd
 		if !m.pwLoading {
@@ -407,6 +450,8 @@ func (m Model) handleKey(msg tea.KeyMsg) (Model, tea.Cmd) {
 		return m.handleAPIKeyMenuKey(msg)
 	case modePasswordSet:
 		return m.handlePasswordKey(msg)
+	case modeLogin:
+		return m.handleLoginKey(msg)
 	case modeAPIKeyCreate:
 		return m.handleAPIKeyCreateKey(msg)
 	case modeAPIKeyReveal:
@@ -456,6 +501,13 @@ func (m Model) handleDashboardKey(msg tea.KeyMsg) (Model, tea.Cmd) {
 		}
 		return m, nil
 
+	case "L":
+		if !m.connected {
+			return m, nil
+		}
+		m.statusMsg = "Signing out…"
+		return m, logoutCmd(m.client)
+
 	case "T":
 		if !m.connected || len(m.teams) == 0 {
 			return m, nil
@@ -1397,3 +1449,119 @@ func (m Model) handlePasswordKey(msg tea.KeyMsg) (Model, tea.Cmd) {
 	}
 	return m, nil
 }
+
+// ── Sign in ───────────────────────────────────────────────────────────────────
+
+// msgError digs the error out of the messages that carry one, so the 401 check
+// in Update covers them all in one place.
+func msgError(msg tea.Msg) error {
+	switch msg := msg.(type) {
+	case connectErrMsg:
+		return msg.err
+	case fetchDataErrMsg:
+		return msg.err
+	case detailErrMsg:
+		return msg.err
+	case actionErrMsg:
+		return msg.err
+	case detailStatsErrMsg:
+		return msg.err
+	case scheduleFetchErrMsg:
+		return msg.err
+	case scheduleActionErrMsg:
+		return msg.err
+	case userActionErrMsg:
+		return msg.err
+	}
+	return nil
+}
+
+// requireLogin returns to the sign-in form with everything the previous session
+// loaded dropped, so a different account never sees the last one's incidents.
+func (m Model) requireLogin(note string) Model {
+	name := m.loginInputs[loginUsername].Value()
+	fresh := NewModel(m.client, m.serverURL, m.refreshInterval, m.theme)
+	fresh.width, fresh.height = m.width, m.height
+	fresh.defaultTeam = m.defaultTeam
+	fresh.ticking = m.ticking
+	fresh.mode = modeLogin
+	fresh.loginInputs[loginUsername].SetValue(name)
+	fresh.loginNote = note
+	fresh.focusLogin(loginUsername)
+	if name != "" {
+		fresh.focusLogin(loginPassword)
+	}
+	fresh.rebuildIncidentTable()
+	fresh.rebuildTable()
+	fresh.rebuildArchivedTable()
+	fresh.rebuildScheduleTable()
+	fresh.rebuildUserPickerTable()
+	fresh.rebuildUserManageTable()
+	return fresh
+}
+
+func (m *Model) blurLoginForm() {
+	for i := range m.loginInputs {
+		m.loginInputs[i].Blur()
+	}
+}
+
+func (m *Model) focusLogin(field int) {
+	m.blurLoginForm()
+	m.loginFocus = field
+	m.loginInputs[field].Focus()
+}
+
+// loginErrorText turns a failed sign-in into something to act on. The server
+// answers a wrong password, an unknown user and an account with no password with
+// the same 401, so the last one has to be named here or it reads as a typo.
+func loginErrorText(err error) string {
+	var se *api.StatusError
+	if errors.As(err, &se) {
+		switch se.Code {
+		case http.StatusUnauthorized:
+			return "invalid username or password — an account with no password cannot sign in; set one in the web UI first"
+		case http.StatusTooManyRequests:
+			return "too many attempts — wait a few minutes and try again"
+		}
+	}
+	return err.Error()
+}
+
+func (m Model) handleLoginKey(msg tea.KeyMsg) (Model, tea.Cmd) {
+	switch msg.String() {
+	case "ctrl+c", "esc":
+		return m, tea.Quit
+	}
+	if m.loggingIn {
+		return m, nil
+	}
+
+	switch msg.String() {
+	case "tab", "shift+tab", "down", "up":
+		next := loginPassword
+		if m.loginFocus == loginPassword {
+			next = loginUsername
+		}
+		m.focusLogin(next)
+		return m, nil
+
+	case "enter":
+		username := strings.TrimSpace(m.loginInputs[loginUsername].Value())
+		password := m.loginInputs[loginPassword].Value()
+		switch {
+		case username == "":
+			m.loginErr = "enter your username"
+			m.focusLogin(loginUsername)
+			return m, nil
+		case password == "":
+			m.loginErr = "enter your password"
+			m.focusLogin(loginPassword)
+			return m, nil
+		}
+		m.loggingIn = true
+		m.loginErr = ""
+		return m, loginCmd(m.client, m.serverURL, username, password)
+	}
+	return m, nil
+}
diff --git a/internal/tui/view.go b/internal/tui/view.go
index 5337944..069e349 100644
--- a/internal/tui/view.go
+++ b/internal/tui/view.go
@@ -34,6 +34,25 @@ func (m Model) renderHeader() string {
 	return spread(title, right, m.width)
 }
 
+// renderLogin is the sign-in form. It is the whole body: nothing else is shown
+// until the server has accepted a session.
+func (m Model) renderLogin() string {
+	var b strings.Builder
+	b.WriteString("\n  " + m.styles.Bold.Render("Sign in to "+m.serverURL) + "\n\n")
+	if m.loginNote != "" {
+		b.WriteString(m.styles.Status.Render("  "+m.loginNote) + "\n\n")
+	}
+	b.WriteString("  " + m.styles.Header.Render("Username: ") + m.loginInputs[loginUsername].View() + "\n")
+	b.WriteString("  " + m.styles.Header.Render("Password: ") + m.loginInputs[loginPassword].View() + "\n\n")
+	switch {
+	case m.loggingIn:
+		b.WriteString(m.styles.Muted.Render("  Signing in…") + "\n")
+	case m.loginErr != "":
+		b.WriteString(m.styles.Error.Render("  "+m.loginErr) + "\n")
+	}
+	return b.String()
+}
+
 // activeTeamLabel names what the lists are narrowed to.
 func (m Model) activeTeamLabel() string {
 	if t, ok := m.activeTeam(); ok {
@@ -56,6 +75,9 @@ func (m Model) renderTabs() string {
 }
 
 func (m Model) renderBody() string {
+	if m.mode == modeLogin {
+		return m.renderLogin()
+	}
 	if m.err != nil {
 		return "\n" + m.styles.Error.Render(fmt.Sprintf("  Error: %v", m.err)) +
 			"\n" + m.styles.Muted.Render("  Press r to retry.")
@@ -160,10 +182,13 @@ func (m Model) renderFooter() string {
 	case modePasswordSet:
 		return withStatus("  tab·next field  enter·set password  esc·cancel")
 
+	case modeLogin:
+		return "\n" + m.styles.Footer.Render("  tab·next field  enter·sign in  esc·quit")
+
 	default:
 		switch m.activeSection {
 		case sectionIncidents:
-			return withStatus("  enter·detail  x·archive  f·filter  " + m.teamHint() + "r·refresh  tab·section  q·quit")
+			return withStatus("  enter·detail  x·archive  f·filter  " + m.teamHint() + "r·refresh  tab·section  L·sign out  q·quit")
 		case sectionAlerts:
 			return withStatus("  enter·detail  f·filter  " + m.teamHint() + "r·refresh  tab·section  q·quit")
 		case sectionStats:
@@ -173,7 +198,7 @@ func (m Model) renderFooter() string {
 		case sectionSchedule:
 			return withStatus("  +·assign day  W·assign week  d·del  ←/→·shift week  " + m.teamHint() + "tab·section  r·refresh  q·quit")
 		case sectionUsers:
-			return withStatus("  n·new user  t·topic  d·delete  k·API keys  p·password  r·refresh  tab·section  q·quit")
+			return withStatus("  n·new user  t·topic  d·delete  k·API keys  p·password  r·refresh  L·sign out  q·quit")
 		}
 		return "\n" + m.styles.Footer.Render(m.help.ShortHelpView(m.keys.ShortHelp()))
 	}
diff --git a/main.go b/main.go
index 62b83f0..b14d360 100644
--- a/main.go
+++ b/main.go
@@ -7,6 +7,7 @@ import (
 
 	"git.ryuvia.com/niklas/terdut-tui/internal/api"
 	"git.ryuvia.com/niklas/terdut-tui/internal/config"
+	"git.ryuvia.com/niklas/terdut-tui/internal/session"
 	"git.ryuvia.com/niklas/terdut-tui/internal/theme"
 	"git.ryuvia.com/niklas/terdut-tui/internal/tui"
 	"git.ryuvia.com/niklas/terdut-tui/internal/updater"
@@ -45,8 +46,17 @@ func main() {
 		os.Exit(1)
 	}
 
-	client := api.NewClient(cfg.ServerURL, cfg.APIKey)
-	model := tui.NewModel(client, cfg.ServerURL, cfg.RefreshInterval, th).WithDefaultTeam(cfg.Team)
+	client := api.NewClient(cfg.ServerURL)
+	if token := session.Load(cfg.ServerURL); token != "" {
+		client.SetSession(token)
+	}
+	note := ""
+	if cfg.LegacyAPIKey {
+		note = "api_key in config.yaml is no longer used: sign in with your username and password"
+	}
+	model := tui.NewModel(client, cfg.ServerURL, cfg.RefreshInterval, th).
+		WithDefaultTeam(cfg.Team).
+		WithLogin(cfg.Username, note)
 
 	p := tea.NewProgram(model, tea.WithAltScreen())
 	if _, err := p.Run(); err != nil {