Merge pull request #58 from maia-iyer/slack_tool_jwks_validation

⚠️ Slack tool jwks validation

Author: pdettori

mcp/slack_tool/README.md

@@ -12,15 +12,13 @@ You can configure the server with the following environment variables:
 | `SLACK_BOT_TOKEN`        | Yes       | - | Bot token for the Slack server. Required for any functionality |
 | `LOG_LEVEL`              | No        | `DEBUG`                | Application log level |
 | `MCP_TRANSPORT`          | No        | `streamable-http`      | Passed into mcp.run to determine mcp transport |
-| `ISSUER`                 | No        | - | If populated, will publish that it is OAuth-secured by this issuer (but no actual verification). Must be URI format |
-| `INTROSPECTION_ENDPOINT` | No        | - | If populated with `CLIENT_ID` and `CLIENT_SECRET`, will introspect access tokens at this endpoint |
-| `CLIENT_ID`              | No        | - | If populated with `INTROSPECTION_ENDPOINT` and `CLIENT_SECRET`, will introspect access tokens using this as the client id to authenticate |
-| `CLIENT_SECRET`          | No        | - | If populated with `INTROSPECTION_ENDPOINT` and `CLIENT_ID`, will introspect access tokens using this as the client secret to authenticate |
-| `AUDIENCE `              | No        | - | If populated with `INTROSPECTION_ENDPOINT` will perform audience validation |
+| `JWKS_URI`               | No        | - | If populated, will perform token validation using the JWKS endpoint |
+| `ISSUER`                 | No        | - | If populated with `JWKS_URI`, will additionally check the `iss` claim during token validation |
+| `AUDIENCE`               | No        | - | If populated with `JWKS_URI`, will additionally check the `aud` claim during token validation |
 | `ADMIN_SLACK_BOT_TOKEN`  | No        | - | Bot token for Slack server with Admin privileges. Required for fine grained authz |
 | `ADMIN_SCOPE_NAME`       | No        | - | Scope that triggers `ADMIN_SLACK_BOT_TOKEN` to be used |
 
-Note: `ISSUER` only affects the published authorization endpoint. All three of `INTROSPECTION_ENDPOINT`, `CLIENT_ID`, and `CLIENT_SECRET` are required for token validation to occur. `AUDIENCE` enables the additional audience check. 
+Note: `JWKS_URI` triggers token validation at runtime. `ISSUER` and `AUDIENCE` will not affect behavior if `JWKS_URI` is not implemented. 
 
 Note: Fine-grained authz is enabled with `ADMIN_SLACK_BOT_TOKEN` and `ADMIN_SCOPE_NAME`. If a received access token includes the `ADMIN_SCOPE_NAME` as a scope, it will use the `ADMIN_SLACK_BOT_TOKEN`
 

mcp/slack_tool/auth.py

@@ -6,7 +6,7 @@ readme = "README.md"
 requires-python = ">=3.10"
 dependencies = [
     "httpx>=0.28.1",
-    "mcp[cli]>=1.12.3",
+    "fastmcp>=2.12.1",
     "requests>=2.32.3",
     "slack_sdk>=3.36.0",
 ]

mcp/slack_tool/pyproject.toml

@@ -2,11 +2,11 @@
 import sys
 import logging
 from typing import List, Dict, Any
-from mcp.server.fastmcp import FastMCP
-from mcp.server.auth.middleware.auth_context import get_access_token
+from fastmcp import FastMCP
+from fastmcp.server.dependencies import get_access_token, AccessToken
+from fastmcp.server.auth.providers.jwt import JWTVerifier
 from slack_sdk import WebClient
 from slack_sdk.errors import SlackApiError
-from auth import get_token_verifier, get_auth
 
 logger = logging.getLogger(__name__)
 logging.basicConfig(level=os.getenv("LOG_LEVEL", "DEBUG"), stream=sys.stdout, format='%(levelname)s: %(message)s')
@@ -29,15 +29,17 @@ def slack_client_from_bot_token(bot_token):
         logger.exception(f"An unexpected error occurred during Slack client initialization: {e}")
         return None
 
-def get_slack_client(access_token = None):
+def get_slack_client(access_token=None):
     if ADMIN_SLACK_BOT_TOKEN is None:
         logger.debug(f"No ADMIN_SLACK_BOT_TOKEN configured - automatically configuring based on SLACK_BOT_TOKEN. ")
         return slack_client_from_bot_token(SLACK_BOT_TOKEN)
     # we do fine-grained authz
     if access_token is None:
         logger.error(f"ADMIN_SLACK_BOT_TOKEN configured, but no access token passed. ")
         return None
-    access_token_scopes = access_token.scopes
+    
+    # Access token is now claims dict from FastMCP AccessToken
+    access_token_scopes = access_token.get("scope", "").split() if access_token.get("scope") else []
     logger.debug(f"Received scopes: {access_token_scopes}")
     admin_scope = os.getenv("ADMIN_SCOPE_NAME")
     is_admin = admin_scope in access_token_scopes
@@ -47,10 +49,19 @@ def get_slack_client(access_token = None):
     return slack_client_from_bot_token(SLACK_BOT_TOKEN)
 
 
-mcp = FastMCP("Slack", host="0.0.0.0", port=8000,
-              token_verifier=get_token_verifier(),
-              auth=get_auth(),
-        )
+# Create FastMCP app
+# Temporary environment variables to manually create verifier
+verifier = None
+JWKS_URI = os.getenv("JWKS_URI")
+ISSUER = os.getenv("ISSUER")
+AUDIENCE = os.getenv("AUDIENCE")
+if not JWKS_URI is None:
+    verifier = JWTVerifier(
+        jwks_uri = JWKS_URI,
+        issuer = ISSUER,
+        audience = AUDIENCE
+    )
+mcp = FastMCP("Slack", auth=verifier)
 
 @mcp.tool()
 def get_channels() -> List[Dict[str, Any]]:
@@ -59,8 +70,9 @@ def get_channels() -> List[Dict[str, Any]]:
     """
     logger.debug(f"Called get_channels tool")
 
-
-    slack_client = get_slack_client(access_token=get_access_token())
+    # Get the current authenticated user's token using FastMCP 2.0 dependency
+    access_token: AccessToken | None = get_access_token()
+    slack_client = get_slack_client(access_token=access_token.claims if access_token else None)
     if slack_client is None:
         return [{"error": f"Could not start slack client. Check the configured bot token"}]
 
@@ -93,7 +105,8 @@ def get_channel_history(channel_id: str, limit: int = 20) -> List:
     """
     logger.debug(f"Called get_channel_history tool: {channel_id}")
 
-    slack_client = get_slack_client(access_token=get_access_token())
+    access_token: AccessToken | None = get_access_token()
+    slack_client = get_slack_client(access_token=access_token.claims if access_token else None)
     if slack_client is None:
         return [{"error": f"Could not start slack client. Check the configured bot token"}]
 
@@ -115,25 +128,22 @@ def get_channel_history(channel_id: str, limit: int = 20) -> List:
 # transport can be specified with MCP_TRANSPORT env variable (defaults to streamable-http)
 def run_server():
     transport = os.getenv("MCP_TRANSPORT", "streamable-http")
-    mcp.run(transport=transport)
+    host = os.getenv("HOST", "0.0.0.0")
+    port = int(os.getenv("PORT", "8000"))
+    mcp.run(transport=transport, host=host, port=port)
 
 if __name__ == "__main__":
     if SLACK_BOT_TOKEN is None: # default slack token
         logger.warning("Please configure the SLACK_BOT_TOKEN environment variable before running the server")
     elif ADMIN_SLACK_BOT_TOKEN is None: # one token set -> we just validate the JWT
-        logger.info("Configured SLACK_BOT_TOKEN environment variable but not ADMIN_SLACK_BOT_TOKEN; will validate token signature")
+        logger.info("Configured SLACK_BOT_TOKEN environment variable but not ADMIN_SLACK_BOT_TOKEN; all requests will use the `SLACK_BOT_TOKEN` to reach the Slack API")
         logger.info("Starting Slack MCP Server")
         run_server()
     else: # two tokens set -> we validate the JWT and connect to slack based on access token scope
         # check if other required Auth variables are set
-        introspection_endpoint = os.getenv("INTROSPECTION_ENDPOINT")
-        client_id = os.getenv("CLIENT_ID")
-        client_secret = os.getenv("CLIENT_SECRET")
-        expected_audience = os.getenv("AUDIENCE")
-        admin_scope = os.getenv("ADMIN_SCOPE_NAME")
-        issuer = os.getenv("ISSUER")
-        if None in [introspection_endpoint, client_id, client_secret, expected_audience, issuer, admin_scope]:
-            logger.error("Configured ADMIN_SLACK_BOT_TOKEN but not one or more of INTROSPECTION_ENDPOINT, CLIENT_ID, CLIENT_SECRET, AUDIENCE, ISSUER. ")
+        auth = os.getenv("JWKS_URI")
+        if auth is None:
+            logger.error("Configured ADMIN_SLACK_BOT_TOKEN but auth is not configured - fine grained authz requires token validation")
         else: 
             logger.info("Configured two slack tokens; finer-grained authz enabled")
             logger.info("Starting Slack MCP Server")