How Instagit MCP Server Handles 401 Authentication Failures with Token Recovery

When the Instagit MCP server encounters a 401 Unauthorized error, it automatically recovers by refreshing stale anonymous tokens while preserving user-provided API keys and surfacing clear error messages.

The instalabsAI/instagit repository implements a resilient Model Context Protocol (MCP) server that interacts with the Instagit API. Understanding how this server manages authentication failures is critical for building reliable integrations that gracefully handle expired credentials without manual intervention.

Token Lookup and Initial Request Flow

Before every API call, the server invokes getOrCreateToken() in src/token.ts to determine which credential to use. This function implements a priority hierarchy:

• Paid users: Returns the INSTAGIT_API_KEY environment variable (lines 51‑55).
• Anonymous users: Returns the token stored in ~/.instagit/token.json, or null if the file does not exist.

The resolved token is then passed to analyzeRepoStreaming() via callApi(), initiating the request to the Instagit API.

Catching and Handling 401 Errors

The request logic in src/index.ts wraps API calls in a try … catch block specifically designed to intercept authentication failures (lines 73‑78). When an error object contains status === 401, the server enters the authentication‑failure recovery branch.

The first decision point distinguishes between user‑provided API keys and anonymous tokens:

• If process.env.INSTAGIT_API_KEY is present, the server does not discard the key. Instead, it returns a user‑friendly message explaining that the supplied API key was rejected by the API (lines 75‑84).
• If no API key exists, the server assumes the anonymous token in ~/.instagit/token.json has expired and initiates the token recovery sequence.

Token Recovery Process for Anonymous Tokens

When operating without a user‑provided API key, the server executes a three‑step recovery mechanism to restore API access without user intervention.

Clearing the Stale Token

The server immediately invalidates the expired credential by calling clearStoredToken() in src/token.ts (lines 37‑41). This function synchronously deletes the ~/.instagit/token.json file from the local filesystem, ensuring no subsequent requests attempt to reuse the invalid token.

Registering a Fresh Anonymous Token

Next, the server invokes registerAnonymousToken(apiUrl) (lines 60‑78) to obtain a new anonymous credential from the Instagit API. This function:

1. Generates a unique device identifier if one does not exist.
2. Sends a registration request to the Instagit API endpoint.
3. Persists the returned token to ~/.instagit/token.json for future use.
4. Returns the new token string to the caller.

Retrying the Original Request

With the fresh token in hand, the server re‑issues the original API call using callApi(newToken) (lines 88‑98). If this retry succeeds, the server returns the analysis results to the client as if no failure occurred. If the retry fails, the error bubbles up as a standard API error message.

Handling Rejected API Keys

When a user provides an API key via the INSTAGIT_API_KEY environment variable and the Instagit API rejects it, the server takes a conservative approach. Rather than attempting to regenerate or replace the key (which could indicate account suspension or invalid credentials), the server surfaces the failure directly to the user with a descriptive message indicating that the supplied API key was rejected. This prevents accidental token churn and allows the user to correct their environment configuration.

Code Examples

Minimal Client Invoking the ask_repo Tool

The following TypeScript example demonstrates how a client interacts with the Instagit MCP server. If the stored anonymous token is expired, the server automatically handles the 401 recovery without client intervention.

import { McpClient } from "@modelcontextprotocol/sdk/client/mcp";

async function askInstagit(repo: string, prompt: string, ref: string | null = null) {
  const client = new McpClient({ /* connection config */ });

  const response = await client.callTool("instagit", "ask_repo", {
    repo,
    prompt,
    ref,
  });

  console.log(response.content[0].text);
}

// Example: Repository analysis that triggers automatic token refresh
askInstagit(
  "example/example-repo",
  "Summarize the main architecture."
);

Forcing a Manual Token Reset

If you need to manually invalidate the current anonymous token (for example, during debugging or after a suspected compromise), you can invoke the token management utility directly:

import { clearStoredToken } from "./src/token.js";

// Removes ~/.instagit/token.json
clearStoredToken();

// The next MCP request will automatically register a new anonymous token.

Summary

• Dual credential support: The Instagit MCP server distinguishes between user‑provided API keys (INSTAGIT_API_KEY) and locally stored anonymous tokens (~/.instagit/token.json).
• Automatic recovery: When receiving a 401 response with an anonymous token, the server automatically clears the stale token, registers a fresh anonymous token, and retries the original request.
• Conservative API key handling: If a user‑provided API key is rejected, the server surfaces the error immediately without attempting recovery, preventing accidental credential churn.
• Implementation locations: Core logic resides in src/index.ts (error handling and retry logic) and src/token.ts (token lifecycle management).

Frequently Asked Questions

What happens when the Instagit MCP server receives a 401 error?

When the server receives a 401 Unauthorized response, it checks whether the request used a user‑provided API key or an anonymous token. If an API key was used, it returns an error message indicating the key was rejected. If an anonymous token was used, it automatically deletes the stale token, obtains a new anonymous token from the Instagit API, and retries the original request.

How does the server distinguish between user API keys and anonymous tokens?

The server checks for the presence of the INSTAGIT_API_KEY environment variable via getOrCreateToken() in src/token.ts. If this variable exists, the server treats it as a user‑provided API key and does not attempt automatic recovery on 401 errors. If the variable is absent, the server uses the token stored in ~/.instagit/token.json and treats 401 errors as recoverable by refreshing the anonymous token.

Can I force a manual token refresh if authentication keeps failing?

Yes. You can manually invalidate the current anonymous token by calling clearStoredToken() from src/token.ts, which deletes the ~/.instagit/token.json file. The next MCP request will automatically trigger registerAnonymousToken() to obtain a fresh token. If you are using a paid API key via INSTAGIT_API_KEY, you must update the environment variable manually, as the server does not modify user‑provided credentials.

Where are anonymous tokens stored on the local filesystem?

Anonymous tokens are persisted in ~/.instagit/token.json. This file is created by registerAnonymousToken() in src/token.ts when the server first obtains an anonymous token from the Instagit API, and it is deleted by clearStoredToken() when the token becomes invalid or expired.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}