The server returned an error. It is not possible to connect to it at the moment usually.
The previously used credentials had been rejected by the server. That usually means that the user should be asked to provide/correct the credentials.
This is the first attempt to get credentials for the source. It's usually used right after the source is opened and the authentication continues with a stored credentials, if any.
A secured connection failed due to some server-side certificate issues.
A return value when there was no 'credentials-required' signal emitted yet, or a pair 'authenticate' signal had been received. This value should not be used in the call of 'credentials-required'.
An ESource's authentication reason, used by an ESource::CredentialsRequired method.