feat(account): change your own password on the Account page (milestone 497)

Step #5428 "Account page: change your own password" of milestone 497
"Passwords: change your own, and reset it by email". A Password section
in the page's one form, for local accounts: current, new, again. Blank
keeps the password; a new one signs out every other browser
(sessions_since) and keeps this one. A wrong current password counts
toward the login throttle. Audited as account.password_changed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

steward/account/routes.py

@@ -1,8 +1,13 @@
 """The signed-in user's own account (milestone 490): the time zone every
-page writes its times in, and their email (milestone 495). Any role reaches
-it, for themselves only."""
+page writes its times in, their email (milestone 495) and, for a local
+account, their password (milestone 497). Any role reaches it, for
+themselves only."""
 from __future__ import annotations
 
+import time
+from datetime import datetime, timezone
+
+import bcrypt
 from quart import Blueprint, abort, current_app, redirect, render_template, request, session
 
 from steward.auth.middleware import require_role
@@ -14,6 +19,38 @@ account_bp = Blueprint("account", __name__, url_prefix="/account")
 _SOURCES = {"local": "a Steward password", "ldap": "LDAP", "oidc": "single sign-on"}
 
 
+def _password_matches(user: User, password: str) -> bool:
+    try:
+        return bcrypt.checkpw(password.encode(), user.password_hash.encode())
+    except ValueError:                     # not a bcrypt hash: no password matches it
+        return False
+
+
+def _change_password(user: User, form) -> bool:
+    """Apply the Password section: False when it was left blank, True when the
+    password changed; ValueError says why it can't. Every other browser signed
+    in as this account is signed out (#5427)."""
+    from steward.auth.throttle import login_throttle
+    from steward.core.proxy import client_ip
+    from steward.settings.users import _hash, password_problem
+    new = form.get("new_password") or ""
+    if not new or user.auth_source != "local":
+        return False
+    ip = client_ip()
+    if login_throttle.retry_after(ip, current_app.config.get("LOGIN_MAX_FAILURES", 5),
+                                  current_app.config.get("LOGIN_LOCKOUT_MINUTES", 15) * 60):
+        raise ValueError("Too many wrong passwords from this address. Try again later.")
+    if not _password_matches(user, form.get("current_password") or ""):
+        login_throttle.failed(ip)
+        raise ValueError("Your current password isn't right, so nothing was saved.")
+    problem = password_problem(new, form.get("new_confirm") or "")
+    if problem:
+        raise ValueError(problem)
+    user.password_hash = _hash(new)
+    user.sessions_since = datetime.now(timezone.utc)
+    return True
+
+
 async def _me(db) -> User:
     # A share link opens widgets read-only; it has no account.
     user_id = session.get("user_id")
@@ -39,15 +76,25 @@ async def account(error: str | None = None, status: int = 200):
         "account/index.html", user=user, source=_SOURCES.get(user.auth_source, user.auth_source),
         zone_name=zone_name, zone_title=zone_name.split("/", 1)[-1].replace("_", " "),
         zone_label=formatting.tz_label(tz), zones=formatting.zones_by_region(),
-        defaults=defaults, error=error), status
+        defaults=defaults, error=error, min_password=_min_password(),
+        done=_DONE.get(request.args.get("done", ""))), status
+
+
+_DONE = {"saved": "Saved.",
+         "password": "Saved. Your password is changed; anywhere else you were signed in, you're signed out."}
+
+
+def _min_password() -> int:
+    from steward.settings.users import MIN_PASSWORD
+    return MIN_PASSWORD
 
 
 @account_bp.post("/")
 @require_role(UserRole.viewer)
 async def account_save():
-    """The page's one form: your time zone, your address and whether you're
-    emailed alerts and the weekly report (milestone 495). Nothing is saved
-    unless all of it is valid."""
+    """The page's one form: your time zone, your address, whether you're
+    emailed alerts and the weekly report (milestone 495), and a new password
+    (milestone 497). Nothing is saved unless all of it is valid."""
     from sqlalchemy.exc import IntegrityError
     from steward.core.audit import log_audit
     from steward.core.mail import apply_email_form
@@ -64,17 +111,21 @@ async def account_save():
                     raise ValueError(error)
                 before = user.time_zone
                 user.time_zone = name
+                password_changed = _change_password(user, form)
     except ValueError as exc:
         return await account(str(exc), 400)
     except IntegrityError:
         return await account("Another account already uses that address.", 400)
     session["tz"] = name
+    if password_changed:
+        session["login_at"] = time.time()      # this session carries on under the new password
+        await log_audit(current_app, user.id, user.username, "account.password_changed")
     if before != name:
         await log_audit(current_app, user.id, user.username, "account.time_zone",
                         detail={"time_zone": name, "was": before or "UTC"})
     if changes:
         await log_audit(current_app, user.id, user.username, "account.email", detail=changes)
-    return redirect("/account/")
+    return redirect("/account/?done=" + ("password" if password_changed else "saved"))
 
 
 @account_bp.post("/time-zone/adopt")