Issue when connecting to open shift via mysql workbench on Mac
The error message tells you that the MySQL server is not accepting a connection for user adminM4B1hN at the given host. You need to allow such a connection for that user (e.g. by adding an anyhost user entry (adminM4B1hN@%) for that user.

Also, keep in mind how the MySQL server is seen from the remote end of your SSH tunnel. If the tunnel ends on the same machine where the MySQL runs then the MySQL server address would be localhost not what you have given. The address is always resolved relative to the remote end of the tunnel.