credentials: Move user impersonation to peer::get_identity()

To retrieve user credentials, EapHost provides us the interactive user's
token we can use to impersonate.

By doing the impersonation early in peer::get_identity(), we don't need
to pass the token down the lower methods. This is rather a
simplification than a performance optimization.

Signed-off-by: Simon Rozman <simon@rozman.si>

lib/TLS/src/Credentials.cpp

@@ -267,7 +267,6 @@ std::wstring eap::credentials_tls::get_identity() const
 
 eap::credentials::source_t eap::credentials_tls::combine(
     _In_             DWORD         dwFlags,
-    _In_opt_         HANDLE        hTokenImpersonateUser,
     _In_opt_   const credentials   *cred_cached,
     _In_       const config_method &cfg,
     _In_opt_z_       LPCTSTR       pszTargetName)
@@ -290,9 +289,6 @@ eap::credentials::source_t eap::credentials_tls::combine(
     }
 
     if (pszTargetName) {
-        // Switch user context.
-        user_impersonator impersonating(hTokenImpersonateUser);
-
         try {
             credentials_tls cred_loaded(m_module);
             cred_loaded.retrieve(pszTargetName, cfg.m_level);