The credentials_required signal is emitted when the source requires credentials to connect to
(possibly remote) data store.
The credentials can be passed to the backend using invoke_authenticate function.
| reason |
an SourceCredentialsReason indicating why the credentials are requested |
| certificate_pem |
PEM-encoded secure connection certificate for failed SSL/TLS checks |
| certificate_errors |
what failed with the SSL/TLS certificate |
| error |
a text description of the error, if any |