It's not possible to directly extract a username or password from CredentialCache.DefaultCredentials because the password is not stored in a way that can be directly retrieved.
DefaultCredentials is used for authentication. by the operating system and represents the system's credentials for the current security context.

See usage:
https://learn.microsoft.com/en-us/dotnet/api/system.net.credentialcache.defaultcredentials?view=net-9.0

For more control over credentials, use NetworkCredential or try impersonation techniques.