Host LogicApps as an MCP Server on Azure Container Apps

#mcp #logicapps #azure

Host an MCP Server on ACA and Consume It from a Logic App Agent

Run Logic Apps Standard as an MCP server in a Docker container on Azure Container Apps — then call it from another Logic App using the built-in MCP client connector inside an agent loop.

This post connects two earlier pieces:

MCP server setup: Logic Apps ❤️ MCP — Expose Arithmetic Tools — enabling the /api/mcp endpoint and testing the tools
Running on ACA: Logic Apps Standard on ACA — we take the same MCP server principles and host it as a Docker container on Azure Container Apps

If you haven't read those, here's what's already running before this post starts.

What's already deployed

Seven arithmetic workflows — add, sub, mul, div, mod, pow, sqrt — each an HTTP trigger workflow that takes inputs and returns a result. They're baked into a Docker image and running as a single container on ACA.

One block in host.json enables the MCP endpoint:

"workflow": {
  "McpServerEndpoints": {
    "enable": true,
    "authentication": { "type": "anonymous" }
  }
}

The runtime exposes each workflow as an MCP tool automatically. No extra code, no separate service — the container itself is the MCP server, reachable at:

https://la-arithmeticmcp.<env>.westeurope.azurecontainerapps.io/api/mcp

All seven tools are immediately discoverable:

Consuming it from another Logic App

A second Logic App — BODMASAgent — receives a math expression via HTTP and uses an Agent action (Azure OpenAI) to solve it. The agent has one tool available: the MCP server connector pointing at the endpoint above.

When you add the MCP server action inside the Agent loop and connect it to the endpoint, the designer auto-discovers all tools and lets you pick which ones the agent can call:

POST (2 + 3) * 4^2 / 2 and the agent works through BODMAS order on its own, calling one tool per step:

✅ Step 1: (2 + 3) = 5   → wf_arithmetic_add
✅ Step 2: 4² = 16        → wf_arithmetic_pow
✅ Step 3: 5 × 16 = 80    → wf_arithmetic_mul
✅ Step 4: 80 ÷ 2 = 40    → wf_arithmetic_div
✅ Final Answer: 40

No orchestration code in the consuming Logic App. The agent decides the order and arguments; each tool call triggers a real workflow run on the server container and returns the result.

Securing the MCP endpoint on ACA

The host.json above sets "type": "anonymous" — fine for local dev and demos, but for production you want the endpoint protected.

ACA doesn't have App Service Easy Auth built in, but it has its own ingress-level authentication that works the same way: the ACA runtime validates the Azure AD Bearer token before the request reaches the container. The Logic App MCP endpoint stays anonymous internally; ACA acts as the auth gateway.

Setup — two steps:

Create an Azure AD app registration (la-arithmeticmcp-auth) and create a service principal for it in the tenant:

az ad sp create --id <app-id>

Enable ACA auth and point it at the app registration:

az containerapp auth update \
  --name la-arithmeticmcp --resource-group LogicAppHubRG \
  --enabled true --action Return401

az containerapp auth microsoft update \
  --name la-arithmeticmcp --resource-group LogicAppHubRG \
  --client-id <app-id> \
  --tenant-id <tenant-id> \
  --allowed-audiences "api://<app-id>"

Getting a token (client credentials):

curl -X POST "https://login.microsoftonline.com/<tenant-id>/oauth2/v2.0/token" \
  --data-urlencode "grant_type=client_credentials" \
  --data-urlencode "client_id=<app-id>" \
  --data-urlencode "client_secret=<secret>" \
  --data-urlencode "scope=api://<app-id>/.default"

Result:

# No token
HTTP 401  ← blocked by ACA ingress

# Valid Bearer token → initialize session
HTTP 200  {"protocolVersion":"2025-06-18","serverInfo":{"name":"Logic Apps Remote MCP Server",...}}

# Session established → tools/list
HTTP 200  {"tools":[{"name":"wf_arithmetic_div",...},{"name":"wf_arithmetic_add",...}]}

The MCP client (Postman, Logic App connector, or any client) just needs to include Authorization: Bearer <token> on every request.