NTSTATUS SamValidateUser(_In_ SECURITY_LOGON_TYPE LogonType, _In_ PUNICODE_STRING LogonUserName, _In_ PUNICODE_STRING LogonDomain, _In_ PLSA_SAM_PWD_DATA LogonPwdData, _In_ PUNICODE_STRING ComputerName, _Out_ PBOOL SpecialAccount, _Out_ PRPC_SID *AccountDomainSidPtr, _Out_ SAMPR_HANDLE *UserHandlePtr, _Out_ PSAMPR_USER_INFO_BUFFER *UserInfoPtr, _Out_ PNTSTATUS SubStatus)
Validates a user by checking if it exists in the sam database. Some other checks are done further.