Add SSE server support

[sibbl]

Is your feature request related to a problem? Please describe.

For now, only the stdio protocol for usage as a server is supported.
However, I'd like to deploy my server on a remote machine and let MCP clients to connect via the SSE transport.
See the protocol page about transport concepts: https://modelcontextprotocol.io/docs/concepts/transports#server-sent-events-sse

Describe the solution you'd like
I'd like to tell the MCP server to simply start an HTTP server on a specific port.

Optionally, further configuration should be possible, including:

• definition of the SSE endpoint URL (/sse by default)
• definition of the message endpoint URL (/messages by default)
• required headers (i.e. for authorization)
• CORS for using it from inside a browser context

Additionally, support for ASP.NET servers would be helpful. A specific ASP.NET package could provide extension methods to register services and a middleware for a WebApplicationBuilder.

Describe alternatives you've considered

Other frameworks for Python and Typescript support this out of the box already. Some samples:

• https://mcp-framework.com/docs/Transports/sse
• https://github.com/punkpeye/fastmcp
• https://github.com/jlowin/fastmcp
• https://github.com/modelcontextprotocol/typescript-sdk

[afrise]

Hey, thanks for opening the issue. SSE is the next thing I am working on adding to the library.

[bitarcher]

Hi @afrise , I also wait for this support. I can't help for integrating it myself, since it seems to be difficult. If you could keep .net 4.8 compatibility while doing this besause your lib seems to be the only advanced library supporting old frameworks.