Antigravity Authentication & Integration Guide

Overview

Antigravity (Google Cloud Code Assist) is a Google-backed AI model provider that offers access to models like Claude Opus 4.6 and Gemini through Google's Cloud infrastructure. This document provides a complete guide on how authentication works, how to fetch models, and how to implement a new provider in PicoClaw.

---

Table of Contents

1. Authentication Flow
2. OAuth Implementation Details
3. Token Management
4. Models List Fetching
5. Usage Tracking
6. Provider Plugin Structure
7. Integration Requirements
8. API Endpoints
9. Configuration
10. Creating a New Provider in PicoClaw

---

Authentication Flow

1. OAuth 2.0 with PKCE

Antigravity uses OAuth 2.0 with PKCE (Proof Key for Code Exchange) for secure authentication:

┌─────────────┐                                    ┌─────────────────┐
│   Client    │ ───(1) Generate PKCE Pair────────> │                 │
│             │ ───(2) Open Auth URL─────────────> │  Google OAuth   │
│             │                                    │    Server       │
│             │ <──(3) Redirect with Code───────── │                 │
│             │                                    └─────────────────┘
│             │ ───(4) Exchange Code for Tokens──> │   Token URL     │
│             │                                    │                 │
│             │ <──(5) Access + Refresh Tokens──── │                 │
└─────────────┘                                    └─────────────────┘

2. Detailed Steps

Step 1: Generate PKCE Parameters

function generatePkce(): { verifier: string; challenge: string } {
  const verifier = randomBytes(32).toString("hex");
  const challenge = createHash("sha256").update(verifier).digest("base64url");
  return { verifier, challenge };
}

Step 2: Build Authorization URL

const AUTH_URL = "https://accounts.google.com/o/oauth2/v2/auth";
const REDIRECT_URI = "http://localhost:51121/oauth-callback";

function buildAuthUrl(params: { challenge: string; state: string }): string {
  const url = new URL(AUTH_URL);
  url.searchParams.set("client_id", CLIENT_ID);
  url.searchParams.set("response_type", "code");
  url.searchParams.set("redirect_uri", REDIRECT_URI);
  url.searchParams.set("scope", SCOPES.join(" "));
  url.searchParams.set("code_challenge", params.challenge);
  url.searchParams.set("code_challenge_method", "S256");
  url.searchParams.set("state", params.state);
  url.searchParams.set("access_type", "offline");
  url.searchParams.set("prompt", "consent");
  return url.toString();
}

Required Scopes:

const SCOPES = [
  "https://www.googleapis.com/auth/cloud-platform",
  "https://www.googleapis.com/auth/userinfo.email",
  "https://www.googleapis.com/auth/userinfo.profile",
  "https://www.googleapis.com/auth/cclog",
  "https://www.googleapis.com/auth/experimentsandconfigs",
];

Step 3: Handle OAuth Callback

Automatic Mode (Local Development):

• Start a local HTTP server on port 51121
• Wait for the redirect from Google
• Extract the authorization code from the query parameters

Manual Mode (Remote/Headless):

• Display the authorization URL to the user
• User completes authentication in their browser
• User pastes the full redirect URL back into the terminal
• Parse the code from the pasted URL

Step 4: Exchange Code for Tokens

const TOKEN_URL = "https://oauth2.googleapis.com/token";

async function exchangeCode(params: {
  code: string;
  verifier: string;
}): Promise<{ access: string; refresh: string; expires: number }> {
  const response = await fetch(TOKEN_URL, {
    method: "POST",
    headers: { "Content-Type": "application/x-www-form-urlencoded" },
    body: new URLSearchParams({
      client_id: CLIENT_ID,
      client_secret: CLIENT_SECRET,
      code: params.code,
      grant_type: "authorization_code",
      redirect_uri: REDIRECT_URI,
      code_verifier: params.verifier,
    }),
  });

  const data = await response.json();
  
  return {
    access: data.access_token,
    refresh: data.refresh_token,
    expires: Date.now() + data.expires_in * 1000 - 5 * 60 * 1000, // 5 min buffer
  };
}

Step 5: Fetch Additional User Data

User Email:

async function fetchUserEmail(accessToken: string): Promise<string | undefined> {
  const response = await fetch(
    "https://www.googleapis.com/oauth2/v1/userinfo?alt=json",
    { headers: { Authorization: `Bearer ${accessToken}` } }
  );
  const data = await response.json();
  return data.email;
}

Project ID (Required for API calls):

async function fetchProjectId(accessToken: string): Promise<string> {
  const headers = {
    Authorization: `Bearer ${accessToken}`,
    "Content-Type": "application/json",
    "User-Agent": "google-api-nodejs-client/9.15.1",
    "X-Goog-Api-Client": "google-cloud-sdk vscode_cloudshelleditor/0.1",
    "Client-Metadata": JSON.stringify({
      ideType: "IDE_UNSPECIFIED",
      platform: "PLATFORM_UNSPECIFIED",
      pluginType: "GEMINI",
    }),
  };

  const response = await fetch(
    "https://cloudcode-pa.googleapis.com/v1internal:loadCodeAssist",
    {
      method: "POST",
      headers,
      body: JSON.stringify({
        metadata: {
          ideType: "IDE_UNSPECIFIED",
          platform: "PLATFORM_UNSPECIFIED",
          pluginType: "GEMINI",
        },
      }),
    }
  );

  const data = await response.json();
  return data.cloudaicompanionProject || "rising-fact-p41fc"; // Default fallback
}

---

OAuth Implementation Details

Client Credentials

Important: These are base64-encoded in the source code for sync with pi-ai:

const decode = (s: string) => Buffer.from(s, "base64").toString();

const CLIENT_ID = decode("<BASE64_ENCODED_CLIENT_ID>");
const CLIENT_SECRET = decode("<BASE64_ENCODED_CLIENT_SECRET>");

OAuth Flow Modes

1. Automatic Flow (Local machines with browser):

   • Opens browser automatically
   • Local callback server captures redirect
   • No user interaction required after initial auth

2. Manual Flow (Remote/headless/WSL2):

   • URL displayed for manual copy-paste
   • User completes auth in external browser
   • User pastes full redirect URL back

function shouldUseManualOAuthFlow(isRemote: boolean): boolean {
  return isRemote || isWSL2Sync();
}

---

Token Management

Auth Profile Structure

type OAuthCredential = {
  type: "oauth";
  provider: "google-antigravity";
  access: string;           // Access token
  refresh: string;          // Refresh token
  expires: number;          // Expiration timestamp (ms since epoch)
  email?: string;           // User email
  projectId?: string;       // Google Cloud project ID
};

Token Refresh

The credential includes a refresh token that can be used to obtain new access tokens when the current one expires. The expiration is set with a 5-minute buffer to prevent race conditions.

---

Models List Fetching

Fetch Available Models

const BASE_URL = "https://cloudcode-pa.googleapis.com";

async function fetchAvailableModels(
  accessToken: string,
  projectId: string
): Promise<Model[]> {
  const headers = {
    Authorization: `Bearer ${accessToken}`,
    "Content-Type": "application/json",
    "User-Agent": "antigravity",
    "X-Goog-Api-Client": "google-cloud-sdk vscode_cloudshelleditor/0.1",
  };

  const response = await fetch(
    `${BASE_URL}/v1internal:fetchAvailableModels`,
    {
      method: "POST",
      headers,
      body: JSON.stringify({ project: projectId }),
    }
  );

  const data = await response.json();
  
  // Returns models with quota information
  return Object.entries(data.models).map(([modelId, modelInfo]) => ({
    id: modelId,
    displayName: modelInfo.displayName,
    quotaInfo: {
      remainingFraction: modelInfo.quotaInfo?.remainingFraction,
      resetTime: modelInfo.quotaInfo?.resetTime,
      isExhausted: modelInfo.quotaInfo?.isExhausted,
    },
  }));
}

Response Format

type FetchAvailableModelsResponse = {
  models?: Record<string, {
    displayName?: string;
    quotaInfo?: {
      remainingFraction?: number | string;
      resetTime?: string;      // ISO 8601 timestamp
      isExhausted?: boolean;
    };
  }>;
};

---

Usage Tracking

Fetch Usage Data

export async function fetchAntigravityUsage(
  token: string,
  timeoutMs: number
): Promise<ProviderUsageSnapshot> {
  // 1. Fetch credits and plan info
  const loadCodeAssistRes = await fetch(
    `${BASE_URL}/v1internal:loadCodeAssist`,
    {
      method: "POST",
      headers: {
        Authorization: `Bearer ${token}`,
        "Content-Type": "application/json",
      },
      body: JSON.stringify({
        metadata: {
          ideType: "ANTIGRAVITY",
          platform: "PLATFORM_UNSPECIFIED",
          pluginType: "GEMINI",
        },
      }),
    }
  );

  // Extract credits info
  const { availablePromptCredits, planInfo, currentTier } = data;
  
  // 2. Fetch model quotas
  const modelsRes = await fetch(
    `${BASE_URL}/v1internal:fetchAvailableModels`,
    {
      method: "POST",
      headers: { Authorization: `Bearer ${token}` },
      body: JSON.stringify({ project: projectId }),
    }
  );

  // Build usage windows
  return {
    provider: "google-antigravity",
    displayName: "Google Antigravity",
    windows: [
      { label: "Credits", usedPercent: calculateUsedPercent(available, monthly) },
      // Individual model quotas...
    ],
    plan: currentTier?.name || planType,
  };
}

Usage Response Structure

type ProviderUsageSnapshot = {
  provider: "google-antigravity";
  displayName: string;
  windows: UsageWindow[];
  plan?: string;
  error?: string;
};

type UsageWindow = {
  label: string;           // "Credits" or model ID
  usedPercent: number;     // 0-100
  resetAt?: number;        // Timestamp when quota resets
};

---

Provider Plugin Structure

Plugin Definition

const antigravityPlugin = {
  id: "google-antigravity-auth",
  name: "Google Antigravity Auth",
  description: "OAuth flow for Google Antigravity (Cloud Code Assist)",
  configSchema: emptyPluginConfigSchema(),
  
  register(api: PicoClawPluginApi) {
    api.registerProvider({
      id: "google-antigravity",
      label: "Google Antigravity",
      docsPath: "/providers/models",
      aliases: ["antigravity"],
      
      auth: [
        {
          id: "oauth",
          label: "Google OAuth",
          hint: "PKCE + localhost callback",
          kind: "oauth",
          run: async (ctx: ProviderAuthContext) => {
            // OAuth implementation here
          },
        },
      ],
    });
  },
};

ProviderAuthContext

type ProviderAuthContext = {
  config: PicoClawConfig;
  agentDir?: string;
  workspaceDir?: string;
  prompter: WizardPrompter;      // UI prompts/notifications
  runtime: RuntimeEnv;           // Logging, etc.
  isRemote: boolean;             // Whether running remotely
  openUrl: (url: string) => Promise<void>;  // Browser opener
  oauth: {
    createVpsAwareHandlers: Function;
  };
};

ProviderAuthResult

type ProviderAuthResult = {
  profiles: Array<{
    profileId: string;
    credential: AuthProfileCredential;
  }>;
  configPatch?: Partial<PicoClawConfig>;
  defaultModel?: string;
  notes?: string[];
};

---

Integration Requirements

1. Required Environment/Dependencies

• Go ≥ 1.21
• PicoClaw codebase (pkg/providers/ and pkg/auth/)
• crypto and net/http standard library packages

2. Required Headers for API Calls

const REQUIRED_HEADERS = {
  "Authorization": `Bearer ${accessToken}`,
  "Content-Type": "application/json",
  "User-Agent": "antigravity",  // or "google-api-nodejs-client/9.15.1"
  "X-Goog-Api-Client": "google-cloud-sdk vscode_cloudshelleditor/0.1",
};

// For loadCodeAssist calls, also include:
const CLIENT_METADATA = {
  ideType: "ANTIGRAVITY",  // or "IDE_UNSPECIFIED"
  platform: "PLATFORM_UNSPECIFIED",
  pluginType: "GEMINI",
};

3. Model Schema Sanitization

Antigravity uses Gemini-compatible models, so tool schemas must be sanitized:

const GOOGLE_SCHEMA_UNSUPPORTED_KEYWORDS = new Set([
  "patternProperties",
  "additionalProperties",
  "$schema",
  "$id",
  "$ref",
  "$defs",
  "definitions",
  "examples",
  "minLength",
  "maxLength",
  "minimum",
  "maximum",
  "multipleOf",
  "pattern",
  "format",
  "minItems",
  "maxItems",
  "uniqueItems",
  "minProperties",
  "maxProperties",
]);

// Clean schema before sending
function cleanToolSchemaForGemini(schema: Record<string, unknown>): unknown {
  // Remove unsupported keywords
  // Ensure top-level has type: "object"
  // Flatten anyOf/oneOf unions
}

4. Thinking Block Handling (Claude Models)

For Antigravity Claude models, thinking blocks require special handling:

const ANTIGRAVITY_SIGNATURE_RE = /^[A-Za-z0-9+/]+={0,2}$/;

export function sanitizeAntigravityThinkingBlocks(
  messages: AgentMessage[]
): AgentMessage[] {
  // Validate thinking signatures
  // Normalize signature fields
  // Discard unsigned thinking blocks
}

---

API Endpoints

Authentication Endpoints

Endpoint	Method	Purpose
https://accounts.google.com/o/oauth2/v2/auth	GET	OAuth authorization
https://oauth2.googleapis.com/token	POST	Token exchange
https://www.googleapis.com/oauth2/v1/userinfo	GET	User info (email)

Cloud Code Assist Endpoints

Endpoint	Method	Purpose
https://cloudcode-pa.googleapis.com/v1internal:loadCodeAssist	POST	Load project info, credits, plan
https://cloudcode-pa.googleapis.com/v1internal:fetchAvailableModels	POST	List available models with quotas
https://cloudcode-pa.googleapis.com/v1internal:streamGenerateContent?alt=sse	POST	Chat streaming endpoint

API Request Format (Chat): The v1internal:streamGenerateContent endpoint expects an envelope wrapping the standard Gemini request:

{
  "project": "your-project-id",
  "model": "model-id",
  "request": {
    "contents": [...],
    "systemInstruction": {...},
    "generationConfig": {...},
    "tools": [...]
  },
  "requestType": "agent",
  "userAgent": "antigravity",
  "requestId": "agent-timestamp-random"
}

API Response Format (SSE): Each SSE message (data: {...}) is wrapped in a response field:

{
  "response": {
    "candidates": [...],
    "usageMetadata": {...},
    "modelVersion": "...",
    "responseId": "..."
  },
  "traceId": "...",
  "metadata": {}
}

---

Configuration

config.json Configuration

{
  "model_list": [
    {
      "model_name": "gemini-flash",
      "model": "antigravity/gemini-3-flash",
      "auth_method": "oauth"
    }
  ],
  "agents": {
    "defaults": {
      "model": "gemini-flash"
    }
  }
}

Auth Profile Storage

Auth profiles are stored in ~/.picoclaw/auth.json:

{
  "credentials": {
    "google-antigravity": {
      "access_token": "ya29...",
      "refresh_token": "1//...",
      "expires_at": "2026-01-01T00:00:00Z",
      "provider": "google-antigravity",
      "auth_method": "oauth",
      "email": "user@example.com",
      "project_id": "my-project-id"
    }
  }
}

---

Creating a New Provider in PicoClaw

PicoClaw providers are implemented as Go packages under pkg/providers/. To add a new provider:

Step-by-Step Implementation

1. Create Provider File

Create a new Go file in pkg/providers/:

pkg/providers/
└── your_provider.go

2. Implement the Provider Interface

Your provider must implement the Provider interface defined in pkg/providers/types.go:

package providers

type YourProvider struct {
    apiKey  string
    apiBase string
}

func NewYourProvider(apiKey, apiBase, proxy string) *YourProvider {
    if apiBase == "" {
        apiBase = "https://api.your-provider.com/v1"
    }
    return &YourProvider{apiKey: apiKey, apiBase: apiBase}
}

func (p *YourProvider) Chat(ctx context.Context, messages []Message, tools []Tool, cb StreamCallback) error {
    // Implement chat completion with streaming
}

3. Register in the Factory

Add your provider to the protocol switch in pkg/providers/factory.go:

case "your-provider":
    return NewYourProvider(sel.apiKey, sel.apiBase, sel.proxy), nil

4. Add Default Config (Optional)

Add a default entry in pkg/config/defaults.go:

{
    ModelName: "your-model",
    Model:     "your-provider/model-name",
    APIKey:    "",
},

5. Add Auth Support (Optional)

If your provider requires OAuth or special authentication, add a case to cmd/picoclaw/cmd_auth.go:

case "your-provider":
    authLoginYourProvider()

6. Configure via config.json

{
  "model_list": [
    {
      "model_name": "your-model",
      "model": "your-provider/model-name",
      "api_key": "your-api-key",
      "api_base": "https://api.your-provider.com/v1"
    }
  ]
}

---

Testing Your Implementation

CLI Commands

# Authenticate with a provider
picoclaw auth login --provider your-provider

# List models (for Antigravity)
picoclaw auth models

# Start the gateway
picoclaw gateway

# Run an agent with a specific model
picoclaw agent -m "Hello" --model your-model

Environment Variables for Testing

# Override default model
export PICOCLAW_AGENTS_DEFAULTS_MODEL=your-model

# Override provider settings
export PICOCLAW_MODEL_LIST='[{"model_name":"your-model","model":"your-provider/model-name","api_key":"..."}]'

---

References

• Source Files:

  • pkg/providers/antigravity_provider.go - Antigravity provider implementation
  • pkg/auth/oauth.go - OAuth flow implementation
  • pkg/auth/store.go - Auth credential storage (~/.picoclaw/auth.json)
  • pkg/providers/factory.go - Provider factory and protocol routing
  • pkg/providers/types.go - Provider interface definitions
  • cmd/picoclaw/cmd_auth.go - Auth CLI commands

• Documentation:

  • docs/ANTIGRAVITY_USAGE.md - Antigravity usage guide
  • docs/migration/model-list-migration.md - Migration guide

---

Notes

1. Google Cloud Project: Antigravity requires Gemini for Google Cloud to be enabled on your Google Cloud project
2. Quotas: Uses Google Cloud project quotas (not separate billing)
3. Model Access: Available models depend on your Google Cloud project configuration
4. Thinking Blocks: Claude models via Antigravity require special handling of thinking blocks with signatures
5. Schema Sanitization: Tool schemas must be sanitized to remove unsupported JSON Schema keywords

---

---

Common Error Handling

1. Rate Limiting (HTTP 429)

Antigravity returns a 429 error when project/model quotas are exhausted. The error response often contains a quotaResetDelay in the details field.

Example 429 Error:

{
  "error": {
    "code": 429,
    "message": "You have exhausted your capacity on this model. Your quota will reset after 4h30m28s.",
    "status": "RESOURCE_EXHAUSTED",
    "details": [
      {
        "@type": "type.googleapis.com/google.rpc.ErrorInfo",
        "metadata": {
          "quotaResetDelay": "4h30m28.060903746s"
        }
      }
    ]
  }
}

2. Empty Responses (Restricted Models)

Some models might show up in the available models list but return an empty response (200 OK but empty SSE stream). This usually happens for preview or restricted models that the current project doesn't have permission to use.

Treatment: Treat empty responses as errors informing the user that the model might be restricted or invalid for their project.

---

Troubleshooting

"Token expired"

• Refresh OAuth tokens: picoclaw auth login --provider antigravity

"Gemini for Google Cloud is not enabled"

• Enable the API in your Google Cloud Console

"Project not found"

• Ensure your Google Cloud project has the necessary APIs enabled
• Check that the project ID is correctly fetched during authentication

Models not appearing in list

• Verify OAuth authentication completed successfully
• Check auth profile storage: ~/.picoclaw/auth.json
• Re-run picoclaw auth login --provider antigravity