Implementing a Secure MCP Server
An MCP server often starts with a seemingly simple requirement: an AI host should find and summarise tickets about a topic. Once current domain data enters a model context, the endpoint is no longer the central question. What matters is which data becomes visible, under whose permissions it is searched, and which actions the server is allowed to expose at all. This question arose while…
Implementing a secure MCP server for an AI application involves careful consideration of access controls, permissions, and the boundaries of the server's capabilities. The MCP server should not become an open API or autonomous agent layer, but rather a read-only component that exposes a limited set of tools to interact with domain data.
For Lutions, a private development project, the decision was made to start with six read-only tools that allow searching for visible tickets, loading individual or multiple tickets, and returning bounded comments, links, or a compact context bundle. These tools are described as read-only to reduce uncertainties and manage security risks. The server's capabilities are separated into tools, prompts, and resources, with tools being the model-controlled interface for accessing domain resources and prompts.
Each tool in the MCP server has a specific contract, such as the `search_zockets` tool, which accepts bounded search text, result limits, and optional filters. This contract prevents the tool from becoming a "perform arbitrary access" function, ensuring that the server does not grant unbounded access to information. Server-side validation and user context still determine which results can be returned.
The process of handling user requests involves using the search tool first to find visible candidates, followed by retrieving targeted context using the `get_zocket_context_bundle` tool. The model's answer is then created from this limited material. This approach prevents a model from misunderstanding content and ensures that requests do not begin with unbounded access to all tickets or blanket full-text exports.
Permissions for the MCP connection are managed through existing API-token authentication, with read access limited to issues:read domain permissions. Project-bound tokens are enforced over MCP, and the endpoint has its own rate limit. The MCP server does not create its own trust zone or invent its own permission model, but rather translates requests into domain operations and respects the same boundaries as outside MCP.
In summary, implementing a secure MCP server involves defining read-only tools, clearly separating tools, prompts, and resources, and ensuring that permissions remain in the domain system. This approach prevents misuse, reduces the attack surface, and maintains the integrity of the data access and actions required by the system.
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