Extending Subgraph Checks in Cosmo

Cosmo's new feature, subgraph check extensions, allows users to implement custom validation logic during subgraph checks by sending check data to an external service and integrating the results with Cosmo’s existing lint checks. This feature was developed in response to customer requests for more customizable checks beyond the default rules, such as specific naming conventions and patterns not included by default. Available under the enterprise license, it operates by sending a request to a configured endpoint in two stages, where the external service processes the data, performs checks, and sends back a response indicating success or failure. Users can configure which data is sent, including composed SDL, lint warnings, schema changes, and more, with security ensured by an HMAC signature for request verification. This system enables teams to use any backend technology for their checks and ensures that only authorized personnel can configure or view the extensions, maintaining existing permissions and separations.