Function withOAuth

Creates a fetch wrapper that handles OAuth authentication automatically.

This wrapper will:

• Add Authorization headers with access tokens
• Handle 401 responses by attempting re-authentication
• Retry the original request after successful auth
• Handle OAuth errors appropriately (OAuthErrorCode.InvalidClient, etc.)

The baseUrl parameter is optional and defaults to using the domain from the request URL. However, you should explicitly provide baseUrl when:

• Making requests to multiple subdomains (e.g., api.example.com, cdn.example.com)
• Using API paths that differ from OAuth discovery paths (e.g., requesting /api/v1/data but OAuth is at /)
• The OAuth server is on a different domain than your API requests
• You want to ensure consistent OAuth behavior regardless of request URLs

For MCP transports, set baseUrl to the same URL you pass to the transport constructor.

Note: This wrapper is designed for general-purpose fetch operations. MCP transports (SSE and StreamableHTTP) already have built-in OAuth handling and should not need this wrapper.