Register an external REST API as a Salesforce External Service and invoke it from Apex

In-depth guide

Steps

1. In Setup > Integrations > External Services, click Add an External Service and provide the named credential and an OpenAPI schema URL or paste the schema directly
2. Salesforce validates the schema and generates Apex classes in the ExternalService namespace; confirm the generated class and method names in the External Services list
3. In Apex, instantiate the generated class (e.g., ExternalService.MyService client = new ExternalService.MyService()) and call the generated method corresponding to the API operation
4. Pass input parameters as a typed request object generated alongside the client class; retrieve the response via the typed response object — no raw HTTP or JSON parsing needed
5. Handle the generated ExternalService.MyService.MyOperation_Response object, checking its Code property for HTTP status and accessing typed body fields directly
6. For operations requiring dynamic headers not expressible in the named credential, use a named credential with a per-user principal to inject user-specific tokens at runtime