Feature/mcp transport context for http servlet sse server transport provider

[stantonk]

NOTE: this is also a pending PR to upstream (modelcontextprotocol#477), but we can't wait.

Implements modelcontextprotocol#476.

Motivation and Context

modelcontextprotocol#420 introduced McpTransportContext.

McpTransportContext should be supported in HttpServletSseServerTransportProvider to enable those who are still on that transport to leverage McpTransportContext to set attributes that Tools, etc. have access to. This is crucial for implementing Authentication & Authorization at the Tool level.

Current Behavior

McpTransportContext is absent from HttpServletSseServerTransportProvider

Context

How has this issue affected you?

We're not able to switch to HttpServletStreamableServerTransportProvider yet, but wish to use McpTransportContext instead of our custom built similar capability.

What are you trying to accomplish?

Authn/z at Tool level.

How Has This Been Tested?

• In a langchain4j agent application calling into a Dropwizard application serving MCP using HttpServletSseServerTransportProvider
• directly by testing a Dropwizard application serving MCP using HttpServletSseServerTransportProvider
• Integration tests included with PR

Breaking Changes

No, use of the McpTransportContext is optional.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

None