Support for SCRAM password authentication was introduced in PostgreSQL 10; PostgreSQL 14 defaults to using scram-sha-256 for password hashing by default:

Change the default of the password_encryption server parameter to scram-sha-256

While the md5 is still supported, it is gradually being phased out in favor of SCRAM.

If you need some reference implementations beyond the PostgreSQL source, here is a list of known PostgreSQL drivers + SCRAM status ( I also have a presentation on the topic that shows the workflow).