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Overview

Antigravity authentication enables access to Antigravity’s AI services through OAuth 2.0. The CLI Proxy API handles the complete OAuth flow with automatic project discovery and token management.

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Prerequisites

Before authenticating with Antigravity, ensure you have:
  • An Antigravity account with API access
  • CLIProxyAPI server installed and configured
  • A web browser for OAuth authentication (or use -no-browser flag)
  • Network access to Antigravity’s authentication servers

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Authentication

1

Start the login process

Run the following command to initiate Antigravity OAuth:
./CLIProxyAPI -antigravity-login
This will:
  • Start a local OAuth callback server
  • Open your default web browser automatically
  • Navigate to Antigravity’s OAuth authorization page
2

Complete OAuth authorization

In the browser window:
  1. Sign in to your Antigravity account
  2. Review the requested permissions
  3. Click “Authorize” or “Allow” to grant access
  4. Wait for the automatic redirect to the callback server
3

Automatic project discovery

After OAuth completes, the CLI automatically:
  • Exchanges the authorization code for access tokens
  • Discovers your Antigravity project ID
  • Saves tokens and project metadata
  • Displays your authenticated account label
4

Confirmation

After successful authentication:
Authentication saved to /path/to/auth/antigravity-<identifier>.json
Authenticated as <your-account-label>
Antigravity authentication successful!
Antigravity authentication includes automatic project ID discovery, similar to Google Gemini’s auto-discovery mode. No manual project selection is required.

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Advanced Options

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Manual Browser Authentication

If you’re on a headless server or the browser doesn’t open automatically: 
./CLIProxyAPI -antigravity-login -no-browser
The CLI will display: 
Please visit this URL to authenticate:
https://antigravity.example.com/oauth/authorize?client_id=...
Open the URL manually in a browser on any device and complete the OAuth flow.

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Custom OAuth Callback Port

To use a specific port for the OAuth callback server: 
./CLIProxyAPI -antigravity-login -oauth-callback-port 9000
Use a custom callback port if:
  • The default port is already in use
  • Your firewall blocks the default port
  • You’re running multiple CLI instances
  • You need to match specific network policies

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Combined Options

You can combine flags for specific scenarios: 
# Headless server with custom port
./CLIProxyAPI -antigravity-login -no-browser -oauth-callback-port 8888

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Configuration

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Token Storage Location

Authentication tokens are stored in the configured auth directory:
  • Default location: Set via -auth-dir flag or in config file
  • Filename format: antigravity-<identifier>-<timestamp>.json
  • Example: antigravity-user-1234567890.json

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Token Contents

The stored token file contains:
  • OAuth 2.0 access token
  • Refresh token (if provided by Antigravity)
  • Token type and expiration timestamp
  • Account identifier/label
  • Auto-discovered project ID
  • Authentication metadata

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Project ID Discovery

Antigravity authentication automatically discovers your project ID:
  • No manual project selection required
  • Similar to Gemini’s Google One mode
  • Project ID is fetched from your account metadata
  • Stored in the token file for future use
This streamlines the authentication process compared to providers requiring manual project configuration.

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Multiple Accounts

You can authenticate with multiple Antigravity accounts: 
# First account
./CLIProxyAPI -antigravity-login

# Second account (after first completes)
./CLIProxyAPI -antigravity-login
Each account:
  • Creates a separate token file
  • Has its own project ID
  • Is automatically loaded by the server
  • Participates in credential rotation
Benefits of multiple accounts:
  • Higher effective rate limits
  • Load balancing across credentials
  • Redundancy if one account has issues
  • Separate billing/usage tracking

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Verification

To verify your authentication is working:
1

Check token file exists

ls -la /path/to/auth-dir/antigravity-*.json
You should see your Antigravity token file(s) listed.
2

Verify account label

During authentication, note the account label displayed:
Authenticated as <your-account-label>
This confirms which Antigravity account was authenticated.
3

Start the server

./CLIProxyAPI
The server will:
  • Automatically discover Antigravity token files
  • Load credentials into the credential pool
  • Log successful credential registration
4

Make a test API request

Send a request to test Antigravity access:
curl http://localhost:8080/v1/chat/completions \
  -H "Content-Type: application/json" \
  -d '{
    "model": "antigravity-model",
    "messages": [{"role": "user", "content": "Hello!"}]
  }'

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Troubleshooting

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Browser doesn’t open automatically

Solution: Use the -no-browser flag: 
./CLIProxyAPI -antigravity-login -no-browser
Then manually open the displayed URL in your browser.

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OAuth callback timeout

Cause: Authorization wasn’t completed within the timeout period. Solution:
  • Complete the OAuth flow more quickly
  • Check if your firewall blocks the callback port
  • Ensure localhost/127.0.0.1 is accessible
  • Try a different callback port with -oauth-callback-port

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”Authentication failed” error

Possible causes:
  • Invalid authorization code
  • Network connectivity issues
  • Antigravity service outage
  • Account permissions insufficient
Solution:
  1. Check your network connection
  2. Verify Antigravity services are operational
  3. Ensure your account has API access enabled
  4. Try authenticating again
  5. Check server logs for detailed error messages

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Project ID discovery failed

Cause: Unable to fetch project ID from Antigravity. Solution:
  • Verify your account is properly set up
  • Check if your account has projects configured
  • Contact Antigravity support if the issue persists
  • Review server logs for specific error details

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Port already in use

Cause: The OAuth callback port is occupied by another service. Solution: Use a custom callback port: 
./CLIProxyAPI -antigravity-login -oauth-callback-port 9001

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Token not saving

Cause: Permission issues with the auth directory. Solution: 
# Create directory if missing
mkdir -p /path/to/auth-dir

# Fix permissions
chmod 755 /path/to/auth-dir

# Verify writable
touch /path/to/auth-dir/test && rm /path/to/auth-dir/test

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Wrong account authenticated

Cause: Signed into different Antigravity account in browser. Solution:
  1. Sign out of the current account in your browser
  2. Clear browser cookies for Antigravity
  3. Run -antigravity-login again
  4. Sign in with the correct account
  5. Complete authorization

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Account label not displayed

Cause: Account metadata not available in OAuth response. Solution:
  • This is informational only - authentication still works
  • Check the token file for account identifier
  • Contact Antigravity support if you need label customization

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Token Refresh

Antigravity tokens are automatically refreshed by the server:
  • The server monitors token expiration timestamps
  • Refresh tokens (if provided) are used to obtain new access tokens
  • Refreshed tokens are saved back to the auth directory
  • No manual intervention required
If refresh fails:
  • Check server logs for specific errors
  • Ensure network connectivity to Antigravity
  • Re-authenticate if tokens are invalid or expired

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Re-authentication

To re-authenticate an Antigravity account:
  1. Delete the existing token file: 
    rm /path/to/auth-dir/antigravity-*.json
  2. Run the login command again: 
    ./CLIProxyAPI -antigravity-login
  3. Complete the OAuth flow again
  4. New tokens and project ID will be saved
Re-authentication is useful when:
  • Tokens expire and can’t be refreshed
  • You need to update permissions
  • Your Antigravity account changes
  • You want to switch to a different account

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Security Best Practices

  • Never share token files - They contain full account access credentials
  • Use restrictive permissions - Keep auth directory at 755 and token files at 600
  • Rotate credentials regularly - Re-authenticate periodically for security
  • Monitor usage - Check server logs for unusual authentication activity
  • Secure your auth directory - Back up tokens securely, encrypt if storing remotely
  • Validate OAuth redirects - Don’t manually modify OAuth URLs or parameters
Your Antigravity token files provide full access to your account and API services. Protect them as you would passwords or API keys.

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Project Management

Unlike other providers, Antigravity handles project management automatically:
  • No manual selection - Project ID is auto-discovered
  • Single project per account - Each authenticated account has one project
  • Automatic association - Project ID is linked to your account
  • Transparent to users - No project configuration needed
If you need to use a different project:
  1. Create/switch to a different Antigravity account
  2. Authenticate that account separately
  3. Each account brings its own project

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