MCP C# SDK supports specification version 2025-06-18 and introduces updated authentication, elicitation support, structured tool output, and resource links. The authentication protocol separates authentication server and resource server roles to facilitate integration with OAuth 2.0 and OpenID Connect and to improve flexibility and security for external resource access. Elicitation enables servers to request structured user input during interactions using the ElicitAsync extension method and developer-defined schemas limited to primitive types with optional descriptions. Client applications opt into elicitation via declared capabilities and use ElicitationHandler to gather and return user input. Structured tool output and resource links enhance tool responses for richer context delivery.
One of the most notable updates in this version is the new authentication protocol. It as explained separates the roles of the authentication server and the resource server, making it easier to integrate with widely used standards such as OAuth 2.0 and OpenID Connect. It is stated that the goal is to improve both flexibility and security when managing access to external resources.
Another important feature, as stated in the release, is elicitation support. This addition allows servers to request structured information directly from users during interactions, enabling more dynamic and context-aware AI experiences. On the server side, elicitation is handled through the ElicitAsync extension method, which requires developers to define schemas for the requested input values. These schemas, limited to primitive types such as strings, numbers, and booleans, may also include descriptions to guide users.
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