feat(mcp): add OAuth 2.0 Client Credentials support for MCP server connections

[SyedShahmeerAli12]

Related Issues

• fixes mcp: Implement OAuth 2.1 Grant Flows (Authorization Code + PKCE and Client Credentials) #2546

Proposed Changes

Add OAuth 2.0 Client Credentials grant support for MCP server connections. Both SSEServerInfo and StreamableHttpServerInfo now accept an optional oauth_config field:

from haystack_integrations.tools.mcp import OAuthConfig, StreamableHttpServerInfo
from haystack.utils import Secret

server_info = StreamableHttpServerInfo(
    url="https://my-mcp-server.com/mcp",
    oauth_config=OAuthConfig(
        client_id="my-client-id",
        client_secret=Secret.from_env_var("MCP_CLIENT_SECRET"),
        token_endpoint="https://auth.example.com/oauth/token",
    ),
)

Tokens are cached in memory and refreshed automatically before expiry. Token endpoint discovery via /.well-known/oauth-authorization-server (RFC 8414) is supported when token_endpoint is not provided directly.

How did you test it

• 37 unit tests with mocked HTTP covering all new classes and functions
• 11 integration tests that spin up a real local HTTP server and exercise the full token-fetch and inject path

Notes for the reviewer

No new dependencies httpx is already a transitive dep of the MCP integration.

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added unit tests and updated the docstrings
• I've used one of the conventional commit types for my PR title: feat:

[github-actions]

Heads-up for maintainers

This PR is from a fork and touches integrations whose integration tests require API keys.
Those tests are skipped in CI because fork PRs don't have access to repo secrets for security reasons.

Affected integrations:

• mcp

Please run the integration tests locally (hatch run test:integration inside each folder) before approving.

[github-actions]

Coverage report (mcp)

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
integrations/mcp/src/haystack_integrations/tools/mcp
mcp_tool.py					646-647
oauth.py					175-178
Project Total

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