Gmail OAuth Setup

Headless-friendly OAuth flow for Gmail API access using gog CLI.

Prerequisites

• gog CLI installed (brew install steipete/tap/gogcli)
• Google Cloud project with OAuth credentials (Desktop app type)
• Gmail API enabled in the project

Quick Setup

1. Create Google Cloud Project & Credentials

1. Go to https://console.cloud.google.com
2. Create a new project (or select existing)
3. Enable Gmail API: APIs & Services → Library → search "Gmail API" → Enable
4. Configure OAuth consent screen: APIs & Services → OAuth consent screen
   • Choose "External" user type
   • Fill in app name, user support email
   • Add scopes: gmail.modify (or others as needed)
   • Important: Click "PUBLISH APP" for permanent tokens (see Troubleshooting)
5. Create credentials: APIs & Services → Credentials → Create Credentials → OAuth client ID
   • Application type: Desktop app
   • Download the JSON file

2. Configure gog

gog auth credentials /path/to/client_secret.json
gog auth keyring file  # Use file-based keyring for headless
export GOG_KEYRING_PASSWORD="your-password"  # Add to .bashrc

3. Run Auth Flow

Run scripts/gmail-auth.sh interactively, or:

# Generate URL
scripts/gmail-auth.sh --url

# User opens URL, approves, copies code from localhost redirect
# Exchange code (do this quickly - codes expire in minutes!)
scripts/gmail-auth.sh --exchange CODE EMAIL

4. Verify

gog gmail search 'is:unread' --max 5 --account [email protected]

Troubleshooting

"Access blocked: [app] has not completed the Google verification process"

Cause: App is in "Testing" mode and the Gmail account isn't a test user.

Solutions (choose one): 1. Publish the app (recommended): - Google Cloud Console → APIs & Services → OAuth consent screen - Click "PUBLISH APP" → Confirm - No Google review needed for personal use - Tokens become permanent

1. Add test user:
   • OAuth consent screen → Test users → + ADD USERS
   • Add the Gmail address you're authorizing
   • Tokens still expire in 7 days

"Google hasn't verified this app" warning screen

This is normal for personal apps. Click: 1. Advanced (bottom left) 2. Go to app name

Safe to proceed since you own the app.

Token expires in 7 days

Cause: App is in "Testing" mode.

Fix: Publish the app (see above). Published apps get permanent refresh tokens.

"invalid_request" or "invalid_grant" errors

Causes: - Authorization code expired (they only last a few minutes) - Code was already used - Redirect URI mismatch

Fix: Generate a fresh auth URL and complete the flow quickly. Paste the code immediately after getting it.

"redirect_uri_mismatch" error

Cause: The redirect URI in the token exchange doesn't match what was used in the auth URL.

Fix: This script uses http://localhost. Make sure both the auth URL and exchange use the same redirect URI.

Page hangs after approving permissions (mobile)

Cause: Browser trying to connect to localhost which doesn't exist on phone.

Fix: - Use a desktop browser instead - Or tap the address bar while it's "hanging" - the URL contains the code - The URL will look like: http://localhost/?code=4/0ABC...

Multiple permission checkboxes causing hangs

Cause: Too many OAuth scopes requested.

Fix: Use minimal scopes. gmail.modify alone is usually sufficient and shows just one permission.

Can't find project in Google Cloud Console

Cause: Signed into wrong Google account.

Fix: Check which account owns the project: - Click profile icon (top right) - Switch accounts - Check project dropdown for each account

"invalid_request" with oob redirect (new projects)

Cause: Google deprecated urn:ietf:wg:oauth:2.0:oob for OAuth clients created after 2022.

Fix: Use http://localhost redirect instead (this script's default). After approval, browser redirects to localhost with code in URL.

Scopes Reference

Files

• scripts/gmail-auth.sh — Interactive auth helper

Tips

• Publish your app — Avoids test user limits and 7-day token expiry
• Exchange codes quickly — They expire in minutes
• Use desktop browser — Mobile browsers can be finicky with localhost redirects
• One scope is enough — gmail.modify covers most use cases