LogonUser function

The LogonUser function attempts to log a user on to the local computer. The local computer is the computer from which LogonUser was called. You cannot use LogonUser to log on to a remote computer. You specify the user with a user name and domain and authenticate the user with a plaintext password. If the function succeeds, you receive a handle to a token that represents the logged-on user. You can then use this token handle to impersonate the specified user or, in most cases, to create a process that runs in the context of the specified user.
This function is available in Advapi32.dll.

BOOL LogonUser(
  _In_      LPTSTR lpszUsername,
  _In_opt_  LPTSTR lpszDomain,
  _In_opt_  LPTSTR lpszPassword,
  _In_      DWORD dwLogonType,
  _In_      DWORD dwLogonProvider,
  _Out_     PHANDLE phToken
);

DllCall("advapi32.dll", "boolean", "LogonUser", 
  "str", $lpszUsername,
  "str", $lpszDomain,
  "str", $lpszPassword,
  "dword", $dwLogonType,
  "dword", $dwLogonProvider,
  "handle*", ""
)

ImpersonateLoggedOnUser function

The ImpersonateLoggedOnUser function lets the calling thread impersonate the security context of a logged-on user. The user is represented by a token handle.
This function is available in Advapi32.dll.

BOOL WINAPI ImpersonateLoggedOnUser(
  _In_  HANDLE hToken
);

DllCall("advapi32.dll", "boolean", "ImpersonateLoggedOnUser", "handle", $hToken)

RevertToSelf function

The RevertToSelf function terminates the impersonation of a client application.
This function is available in Advapi32.dll.

BOOL WINAPI RevertToSelf(void);

DllCall("advapi32.dll", "boolean", "RevertToSelf")