I didn't actually figure out how to resolve it. I fiddled around in domains/domain1/config/domain.xml a little, but in the end I think restarting Glassfish did the trick for me.
INFO: RAR7099: The mcf being used to allocate the connection and the MCF in the pool are not equal.
WARNING: RAR5038:Unexpected exception while creating resource for pool aum_pool. Exception : No PasswordCredential found
WARNING: RAR5117 : Failed to obtain/create connection from connection pool [ aum_pool ]. Reason : No PasswordCredential found
WARNING: RAR5114 : Error allocating connection : [Error in allocating a connection. Cause: No PasswordCredential found]
WARNING: java.sql.SQLException: Error in allocating a connection. Cause: No PasswordCredential found