Auth0 applications default to RS256, while legacy HS256 apps sign tokens with the client secret

RS256 verification fetches the tenant public keys from the well-known JWKS endpoint, so a resource server can verify tokens while holding nothing sensitive. HS256 signs with the client secret, which means every service that verifies must hold a credential that can also impersonate the client and mint its own tokens.

Check an application's advanced settings before writing a verifier, because a mismatch produces a signature failure that reads like a key configuration problem. When switching an existing application from HS256 to RS256, tokens already in flight stop verifying at the moment of the change, so deploy verifiers that accept both algorithms first, then flip the application, then remove HS256 once the longest token lifetime has elapsed.