Canvas App MCP Relay for GPT

This project exposes Microsoft's local Canvas Authoring MCP Server as a remote MCP endpoint that can be hosted on Render.

Architecture

GPT / MCP client
      |
      | Streamable HTTP
      v
Render: canvas-mcp-relay
      |
      | authenticated WebSocket
      v
Your computer: local-bridge.js
      |
      | stdio
      v
Microsoft.PowerApps.CanvasAuthoring.McpServer
      |
      v
Power Apps Studio coauthoring session

Render cannot directly edit your Canvas App because the Microsoft Canvas Authoring MCP process and Power Apps Studio session live on your computer. The local bridge is therefore required while you are authoring.

1. Power Apps prerequisites

• Open the target Canvas App in Power Apps Studio.

• Enable Settings -> Updates -> Coauthoring.

• Keep the Studio tab open while working.

• Your Microsoft account must have edit permission to the app.

2. Local prerequisites

• Node.js 20+

• .NET 10 SDK

• dnx available from the .NET 10 SDK

Verify:

node --version
dotnet --list-sdks
dnx --help

The local bridge starts Microsoft's server with:

dnx Microsoft.PowerApps.CanvasAuthoring.McpServer --yes --prerelease --source https://api.nuget.org/v3/index.json

No custom Azure App Registration or client secret is required for the normal interactive Canvas Authoring flow.

3. Deploy to Render

Push this folder to GitHub, then create a Render Web Service from the repository, or use render.yaml.

Required Render environment variables:

RELAY_TOKEN=<long-random-secret>
MCP_PUBLIC=false
BRIDGE_REQUEST_TIMEOUT_MS=120000

Generate a token locally, for example:

openssl rand -hex 32

After deployment your endpoints will look like:

https://YOUR-SERVICE.onrender.com/health
https://YOUR-SERVICE.onrender.com/mcp
wss://YOUR-SERVICE.onrender.com/bridge

4. Run the local bridge

On your development machine:

npm install
CANVAS_STUDIO_URL='PASTE_THE_FULL_POWER_APPS_STUDIO_URL_HERE' \
REMOTE_URL=wss://YOUR-SERVICE.onrender.com/bridge \
RELAY_TOKEN=YOUR_RENDER_RELAY_TOKEN \
npm run bridge

The bridge starts the Microsoft Canvas MCP server, optionally parses CANVAS_STUDIO_URL, connects to that app's coauthoring session, discovers the live MCP tools, and registers them with Render. The Microsoft sign-in UI is still local to your machine.

If you prefer to connect later through GPT, omit CANVAS_STUDIO_URL; the proxied connect tool remains available.

Check:

curl -H "Authorization: Bearer YOUR_RENDER_RELAY_TOKEN" \
  https://YOUR-SERVICE.onrender.com/status

You should see tools such as connect, sync_canvas, compile_canvas, list_controls, and list_data_sources.

5. Connect the Canvas App

If you supplied CANVAS_STUDIO_URL when starting the bridge, this step is automatic. Otherwise, once GPT can see the MCP tools, call the Canvas MCP connect tool with values from your Power Apps Studio URL:

environment_id: Default-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
app_id: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
environment_category: prod

The Microsoft MCP process runs locally, so interactive Microsoft/Entra authentication happens on your machine. Prefer the normal browser/broker flow.

6. Connect GPT

Use this MCP endpoint:

https://YOUR-SERVICE.onrender.com/mcp

The server accepts the relay token as either:

Authorization: Bearer <RELAY_TOKEN>

or, for clients that cannot configure an Authorization header:

https://YOUR-SERVICE.onrender.com/mcp?token=<RELAY_TOKEN>

The query-string option is provided for compatibility but a bearer header is preferred because URLs are more likely to appear in logs/history.

Important ChatGPT limitation

As of August 2026, full custom MCP write/modify actions in ChatGPT are available to Business and Enterprise/Edu workspaces. Pro supports read/fetch only. If your ChatGPT plan cannot invoke write tools, use the same Render MCP endpoint from an OpenAI API application or another full MCP client.

Safety

• Use a DEV/copy of the Canvas App first.

• Do not set MCP_PUBLIC=true on an internet-facing deployment.

• Rotate RELAY_TOKEN if it is exposed.

• Keep one local bridge connected to one Canvas authoring process at a time.

• Keep the Power Apps Studio tab open.

• After compile_canvas, verify the change in Studio and re-sync before considering it persisted.

Current Microsoft preview caveats

The Canvas Authoring MCP feature is still preview. Known issue classes reported in 2026 include:

• compile_canvas / sync_canvas sometimes reporting a successful push that did not persist canonically.

• Problems involving PCF code components and Canvas Components.

• Large screen YAML hitting a per-file compile limit.

• Intel macOS (osx-x64) currently lacking a supported Canvas Authoring MCP runtime package.

• Repeated Entra sign-in prompts after restarting the Microsoft MCP process.

Troubleshooting

/status says bridgeConnected: false

Run npm run bridge on your machine and make sure REMOTE_URL and RELAY_TOKEN are correct.

dnx not found

Install .NET 10 SDK and restart the terminal.

Canvas MCP starts but tools fail

Confirm:

1. Power Apps Studio is open.

2. Coauthoring is enabled.

3. The connect tool was called with the correct environment ID and app ID.

4. You authenticated with an account that can edit the app.

Intel Mac

Microsoft's current preview package has an open issue for osx-x64. Use Apple Silicon, Windows x64/ARM64, or Linux x64/ARM64 until Microsoft ships the missing runtime.