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cedar-policy-mcp-schema-generator-wasm

WASM bindings for cedar-policy-mcp-schema-generator, exposing SchemaGenerator to JavaScript and TypeScript via wasm-bindgen.

This enables Node.js and browser environments to generate Cedar authorization schemas from MCP tool descriptions with the exact same behavior as the Rust implementation, including correct handling of:

• JSON number as Long or Decimal (configurable)
• additionalProperties as Cedar tagged entities
• Namespaced type deduplication for nested objects

Usage

Install the npm package:

npm install @cedar-policy/mcp-schema-generator-wasm

const { generateSchema } = require('@cedar-policy/mcp-schema-generator-wasm');

const stub = `
namespace MyServer {
    @mcp_principal
    entity User;
    @mcp_resource
    entity McpServer;
    action "call_tool" appliesTo {
        principal: [User],
        resource: [McpServer]
    };
}
`;

const tools = JSON.stringify([
  {
    name: 'read_file',
    description: 'Read a file from disk',
    inputSchema: {
      type: 'object',
      properties: { path: { type: 'string' } },
      required: ['path'],
    },
  },
]);

const result = JSON.parse(generateSchema(stub, tools));

if (result.isOk) {
  console.log(result.schema);     // Human-readable .cedarschema
  console.log(result.schemaJson); // JSON for Cedar WASM isAuthorized()
} else {
  console.error(result.error);
}

API

generateSchema(schemaStub, toolsJson, configJson?)

Parameter	Type	Description
schemaStub	string	Cedar schema stub with @mcp_principal and @mcp_resource annotations
toolsJson	string	MCP tool descriptions as JSON (the tools array from tools/list)
configJson	string?	Optional configuration as JSON

Returns: JSON string with fields:

Field	Type	Description
schema	string | null	Generated Cedar schema as .cedarschema text
schemaJson	string | null	Generated schema as JSON (for isAuthorized())
error	string | null	Error message if generation failed
isOk	boolean	Whether generation succeeded

Configuration

{
  "includeOutputs": false,
  "objectsAsRecords": false,
  "eraseAnnotations": true,
  "flattenNamespaces": false,
  "numbersAsDecimal": false,
  "deduplicateEntityTypes": false
}

Option	Default	Description
includeOutputs	false	Include tool output schemas in actions
objectsAsRecords	false	Use records instead of entities for objects without additionalProperties
eraseAnnotations	true	Remove @mcp_* annotations from output
flattenNamespaces	false	Flatten all types into a single namespace
numbersAsDecimal	false	Encode JSON number as Cedar Decimal instead of Long
deduplicateEntityTypes	false	Consolidate identical entity types across tools into the lowest common ancestor namespace

generateRequest(schemaStub, toolsJson, inputJson, principalType, principalId, resourceType, resourceId, configJson?)

Generates Cedar authorization request components from an MCP tool call.

Parameter	Type	Description
schemaStub	string	Cedar schema stub (same as generateSchema)
toolsJson	string	MCP tool descriptions as JSON
inputJson	string	MCP tool call input ({"params": {"tool": "...", "args": {...}}})
principalType	string	Cedar entity type for the principal (e.g., "User")
principalId	string	Principal identifier (e.g., "alice")
resourceType	string	Cedar entity type for the resource (e.g., "McpServer")
resourceId	string	Resource identifier (e.g., "my-server")
configJson	string?	Optional configuration as JSON

Returns: JSON string with fields:

Field	Type	Description
principal	string | null	Principal EntityUID (e.g., MyServer::User::"alice")
action	string | null	Action EntityUID (e.g., MyServer::Action::"read_file")
resource	string | null	Resource EntityUID (e.g., MyServer::McpServer::"my-server")
entitiesJson	string | null	Entities as a JSON array string
error	string | null	Error message if generation failed
isOk	boolean	Whether generation succeeded

Example:

const { generateRequest } = require('@cedar-policy/mcp-schema-generator-wasm');

const stub = `
namespace MyServer {
    @mcp_principal
    entity User;
    @mcp_resource
    entity McpServer;
    action "call_tool" appliesTo {
        principal: [User],
        resource: [McpServer]
    };
}
`;

const tools = JSON.stringify([
  {
    name: 'read_file',
    description: 'Read a file from disk',
    inputSchema: {
      type: 'object',
      properties: { path: { type: 'string' } },
      required: ['path'],
    },
  },
]);

const input = JSON.stringify({
  params: { tool: 'read_file', args: { path: '/etc/config.yaml' } },
});

const result = JSON.parse(
  generateRequest(stub, tools, input, 'User', 'alice', 'McpServer', 'my-server')
);

if (result.isOk) {
  console.log(result.principal);    // MyServer::User::"alice"
  console.log(result.action);       // MyServer::Action::"read_file"
  console.log(result.resource);     // MyServer::McpServer::"my-server"
  console.log(result.entitiesJson); // JSON array of entities for isAuthorized()
} else {
  console.error(result.error);
}

Building

# Install wasm-pack
cargo install wasm-pack

# Build for Node.js
wasm-pack build --target nodejs --scope cedar-policy

# Build for browsers
wasm-pack build --target web --scope cedar-policy

npm Release

The npm package name is:

@cedar-policy/mcp-schema-generator-wasm
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