Add support for token provider

[deyaaeldeen]

Add Token Provider Support for Dynamic Authentication

Overview

This PR introduces a new tokenProvider option to the OpenAI client, enabling dynamic token retrieval for authentication scenarios where API keys need to be refreshed or obtained at runtime.

Changes

New Feature: tokenProvider Option

• Added TokenProvider type definition: () => Promise<AccessToken>
• Added AccessToken interface with token: string property
• Added tokenProvider option to ClientOptions interface
• Implemented token provider logic in the _setToken() method

Key Benefits

1. Dynamic Authentication: Supports scenarios where tokens expire and need to be refreshed
2. Enhanced Security: Tokens can be retrieved just-in-time rather than stored statically
3. Enterprise Integration: Enables integration with corporate identity providers and token management systems
4. Flexible Authentication: Provides an alternative to static API keys for environments requiring dynamic credentials

Implementation Details

Client Construction:

• tokenProvider and apiKey are mutually exclusive - only one can be provided
• If neither is provided, an error is thrown requiring one of the two authentication methods
• Browser usage automatically allowed when using tokenProvider (sets dangerouslyAllowBrowser: true)

Token Management:

• _setToken() method now returns a boolean indicating if a token was successfully retrieved
• Token provider is called on every request preparation via prepareOptions()

Usage Example

const client = new OpenAI({
  tokenProvider: async () => {
    // Fetch token from your auth service
    const response = await fetch('/api/auth/token');
    const data = await response.json();
    return { token: data.access_token };
  }
});

Backward Compatibility

This change is fully backward compatible. Existing code using apiKey continues to work unchanged. The new tokenProvider option is purely additive.

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