Use resource defined by MCP server provider within OAuth2 resource metadata document (RFC 8707, RFC 9728) #961

Current situation

Library initiates OAuth2 workflow with predefined resource as the base url to abide RFC 8707. This violates a possibility where MCP belongs under umbrella of exposed functionalities. RFC 8707 permits it in its second paragraph.

There was already implemented resource discovery from OAuth2 resource metadata document defined by RFC 9728 in PR 937 which can access the exposed resource.

Change

Use resource defined by OAuth2 resource metadata document so the creator of MCP and its provider can control what resource are tokens requested for.

Impact

Breaking change: changes default behavior where base url is utilized always for resource and use defined resource by provider when available.

Tests

2 tests were added:

• OAuth2 resource metadata document is missing,
• OAuth2 resource metadata document declares resources.

PR 937 already handles situations where document has missing resource.

PR: #962