Verify browser credentials in the served build, not only in CI

When browser configuration is embedded during a build, a successful authentication check using the CI runner's environment does not prove the deployed application has the same credentials. Compare the expected public endpoint and key with the JavaScript actually served by the login page, then verify that pair through a read-only authentication endpoint. Repeat this check before reusing an existing deployment: matching source and database identities can still hide stale browser configuration. Artifact matching depends on the bundler's output and is not a substitute for a complete login test.

Applies when: A frontend embeds public authentication configuration during its build. Keywords: browser credentials build artifact preview login stale configuration verification