Specify the database name associated with the user's credentials. If
authSource is unspecified, authSource defaults to the defaultauthdb
specified in the connection string. If defaultauthdb is unspecified,
then authSource defaults to admin.
The PLAIN (LDAP), GSSAPI (Kerberos), and MONGODB-AWS (IAM)
authentication mechanisms require that authSource be set to $external,
as these mechanisms delegate credential storage to external services.
Specify the database name associated with the user's credentials. If authSource is unspecified, authSource defaults to the defaultauthdb specified in the connection string. If defaultauthdb is unspecified, then authSource defaults to admin.
The PLAIN (LDAP), GSSAPI (Kerberos), and MONGODB-AWS (IAM) authentication mechanisms require that authSource be set to $external, as these mechanisms delegate credential storage to external services.
Ignored if no username is provided.