GraphQL Bridge: a REST-to-GraphQL template for custom connectors

July 24, 2026

GraphQL and Power Platform’s Swagger model don’t agree on much. GraphQL sends one POST with a { query, variables } envelope to a single endpoint. Power Platform models operations per path and verb, expects clean request and response schemas, and treats HTTP 200 as success. Point a custom connector straight at a GraphQL API and you get raw query strings in your flows, false successes on failed queries, and response data buried under a data root.

GraphQL Bridge is a reusable script.csx template that reconciles all three. Callers send flat JSON, the script builds the GraphQL envelope, posts it, and returns clean JSON. No GraphQL knowledge is needed in the connector operations, Power Automate, or Copilot Studio.

You can find the complete code in my SharingIsCaring repository.

Why this is needed

Three mismatches between GraphQL and Power Platform’s Swagger model drive the whole script:

How it works

The bridge chooses one of two modes per OperationId.

Mode A — server-defined document (recommended)

Register the GraphQL document in GraphQlDocuments, keyed by OperationId. The connector body passes straight through as GraphQL variables, so the operation looks like a normal typed REST call:

private static readonly Dictionary<string, string> GraphQlDocuments =
    new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase)
{
    ["GetAssetById"] = @"query GetAssetById($id: ID!) {
        asset(id: $id) { id title status createdAt }
    }",
};

// Optional: return exactly the nested object the Swagger schema expects
private static readonly Dictionary<string, string> ResponseRootPaths =
    new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase)
{
    ["GetAssetById"] = "asset",   // returns data.asset instead of the whole data object
};

The caller sends a flat body:

{ "id": "abc123" }

The script wraps it as variables, posts the registered document, and returns data.asset. The maker never sees GraphQL.

Mode B — passthrough

If no document is registered for the OperationId, the body must carry the query itself. Wire this to a generic RunQuery operation for ad-hoc queries:

{
  "query": "query ($id: ID!) { asset(id: $id) { id title } }",
  "variables": { "id": "abc123" }
}

Reserved body keys (query, variables, operationName) are always honored. In Mode A, everything else in the body becomes variables.

Configuration

Four settings control the bridge, all at the top of script.csx:

Auth is untouched. The incoming request already carries the connector’s Authorization header. The script only changes the method, URI path, and content, so credentials flow through automatically.

Error shapes returned

The bridge turns silent GraphQL failures into real HTTP errors your flows can catch:

• Invalid request JSON returns 400 INVALID_JSON
• No query available returns 400 NO_QUERY
• A GraphQL errors array returns 400 GRAPHQL_ERROR, with errors and any partialData
• A non-2xx from the GraphQL server returns the original status, wrapped as HTTP_<code>
• A non-JSON GraphQL response returns 502 INVALID_GRAPHQL_RESPONSE

Using it for a real API

Most GraphQL APIs expose a single endpoint and use a bearer token:

• Host: the API’s host, such as api.example.com
• Path: /graphql (the default GraphQlPath; change it if the API differs)
• Auth: OAuth 2.0 or an API or personal access token, configured as the connector’s security definition

Steps to adapt it:

1. Point the connector host at the API and set GraphQlPath to its GraphQL endpoint path.
2. Add one entry to GraphQlDocuments per typed operation you want to expose, for queries and mutations.
3. Optionally set ResponseRootPaths so each operation returns the exact nested object.
4. Add a generic RunQuery operation for anything not yet modeled (Mode B).

Because the bridge exposes schema-shaped typed operations rather than a raw passthrough, pair each build with full Swagger response schemas so you keep IntelliSense and dynamic value support in Power Automate.

For per-tenant hosts, where the GraphQL host varies per customer (for example, {tenant}.example.com), Power Platform’s Swagger host is static. Bake the host as a replaceable constant in the script and set the request URI there instead of relying on GraphQlPath alone.

Conventions

• Uses this.Context.SendAsync(...), never new HttpClient(), which the runtime blocks
• Fully qualifies Newtonsoft.Json.Formatting to avoid the System.Xml ambiguity
• Requires no connection parameters; the endpoint path is a compile-time constant

Resources

• Template repo: SharingIsCaring/Connector-Code/GraphQL Bridge
• GraphQL specification: spec.graphql.org
• Custom connector C# code reference: Write code in a custom connector