I'm trying to connect to AWS RDS instance with private IP using SSH tunnel. I have no problems with network/credentials - I tested SSH tunnel to my Postgres server using command-line, and I was able to connect. But no luck with PgAdmin - I'm getting a GSSAPI error message (sorry for screenshot, but Pgadmin for Mac doesn't allow me copy-paste text).
That is just log spam. Since it found GSS credentials in the local environment, that is the first thing it tried. But it failed, probably because the server didn't want to use it. So then it moved on to the next method, which was password auth, and that also failed.That is the real error. Look in the server log file to possibly get more details on that failure. The error sent to unauthenticated users is intentionally vague to avoid leaking information.