Coach: sign in with ChatGPT to use your ChatGPT plan instead of an API key

PRIVACY.md

@@ -161,7 +161,9 @@ configure:
 - **AI Coach** — if you enable this feature and supply your own API key,
   summaries of your data are sent to the AI provider you configure (by
   default, OpenAI) to generate coaching responses. Off by default and
-  requires your own API key.
+  requires your own API key, or signing in with ChatGPT, in which case the
+  same data goes to OpenAI under your ChatGPT account. The sign-in tokens are
+  kept in the device keychain/keystore and sent only to OpenAI.
 - **Health app integration** — if you enable it, the App can write derived
   daily metrics to Apple Health or Google Health Connect, which are controlled
   by your device's own OS-level health app, not by us. The App can also *read*

android/app/src/main/AndroidManifest.xml

@@ -344,5 +344,11 @@
         </intent>
         <!-- Health Connect app discovery (for install/status checks). -->
         <package android:name="com.google.android.apps.healthdata" />
+        <!-- Lets url_launcher find a Custom Tabs browser for the "Sign in with
+             ChatGPT" page (LaunchMode.inAppBrowserView); without it Android 11+
+             falls back to a WebView. -->
+        <intent>
+            <action android:name="android.support.customtabs.action.CustomTabsService" />
+        </intent>
     </queries>
 </manifest>

guides/AI_COACH.md

@@ -14,7 +14,31 @@ the provider you configure. Before enabling the feature, check that
 provider's data retention and training policies — or point the app at a
 model you host yourself.
 
-## Setup
+## Use your ChatGPT plan
+
+If you pay for ChatGPT (Plus, Pro and similar plans), you can skip the API
+key: open **AI Coach → settings**, tap **ChatGPT**, then **Continue with
+ChatGPT** and sign in. Eligible coach, briefing and journal requests then use
+the usage included in your ChatGPT plan instead of API billing. Tap **List
+models** and pick one, then **Save**.
+
+- This uses OpenAI's official
+  [Sign in with ChatGPT](https://developers.openai.com/siwc/token-sharing-open-source)
+  for open-source apps. OpenStrap never sees your password, and never charges
+  for it.
+- Set a limit, or disconnect OpenStrap, under
+  [ChatGPT settings → Usage](https://chatgpt.com/settings/usage). The
+  **Manage usage** button in AI settings goes there.
+- When the limit is reached the coach says so and stops; it never quietly
+  switches to an API key.
+- Your questions and the rows the coach reads go to OpenAI under your ChatGPT
+  account, exactly as with an OpenAI API key.
+- **Sign out of ChatGPT** asks OpenAI to revoke the sign-in and clears it from
+  the phone. If the app says revocation wasn't confirmed, also disconnect
+  OpenStrap in ChatGPT settings. The coach then stays off until you sign in
+  again or pick another provider.
+
+## Setup with an API key
 
 <img src="images/ai-coach/settings.png" width="300" align="right">