Empty authorization name for Digest mechanism causes authentication fail

SASL specification says about Authorization Identity String [1]:

If the authorization identity string is absent, the client is requesting to act as the identity the server associates with the client's credentials. An empty string is equivalent to an absent authorization identity.

In case when authentication configuration includes empty name for authorization name then authentication fail. In correct behavior authentication name should be used if authorization name is empty string.

It is caused by passing empty defaultName to NameCallback constructor which results to IllegalArgumentException. Condition in [2] checks only non-null value of authorizationId but it seems it should also check empty name.

It can be reproduced with correctly set wildfly-config.xml (i.e. configuration where authentication succeed) - in case set-authorization-name element with empty string is added to this configuration file then authentication starts to fail.

The same issue can occurs for every supported SASL mechanism. In needs to be revisited.

We request blocker flag since current behavior violates SASL specification.

[1] https://tools.ietf.org/html/rfc4422#section-3.4.1
[2] https://github.com/wildfly-security/wildfly-elytron/blob/596f25e853c8fbae088ff562708def3a43480aeb/src/main/java/org/wildfly/security/sasl/digest/DigestSaslClient.java#L223