VmGuestCredentialsType

Types of guest credentials
USERNAME_PASSWORD : USERNAME_PASSWORD credentials contains the information necessary to authenticate within a guest using a username and password. This method of authentication is stateless. To use USERNAME_PASSWORD, populate userName and password with the appropriate login information.

Once populated, you can use USERNAME_PASSWORD in any guest operations operation.
SAML_BEARER_TOKEN : SAML_BEARER_TOKEN contains the information necessary to authenticate within a guest using a SAML token. SAML Bearer token credentials relies on a guest alias that associates a guest account with the subject and certificate encoded in a SAML Bearer token obtained from the VMware SSO Server.