ORA-12638: Credential retrieval failed in Oracle 19c

Error: ORA-12638: Credential retrieval failed

While connecting SQLPLUS sys@servicename AS SYSDBA will throw the error ORA-12638.

Refer to the article: https://docs.oracle.com/en/database/oracle/oracle-database/21/nfcon/windows-authentication-no-longer-uses-ntlm-by-default-355195897.html

For Microsoft Windows installations with AUTHENTICATION_SERVICES=NTS, starting with this release, the SQLNET.NO_NTLM parameter setting in the sqlnet.ora file will default to TRUE. In previous releases, the default for this parameter was FALSE. NTLM is the Windows Networks LAN Manager authentication service.

With NTS value, the oracle use window domain username/password, that user is not authenticated to login into your Oracle Server.

Solution: To overcome this error we have to update the Client-side SQLNET.ora file by disabling the authentication_service or No_NTLM solutions Choose either of the following:

SQLNET.NO_NTLM=FALSE

OR 

SQLNET.AUTHENTICATION_SERVICES=NONE