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+.. _mozilla_projects_nss_reference_fc_login:
+
+FC_Login
+========
+
+`Name <#name>`__
+~~~~~~~~~~~~~~~~
+
+.. container::
+
+   ``FC_Login()`` - log a user into a token.
+
+`Syntax <#syntax>`__
+~~~~~~~~~~~~~~~~~~~~
+
+.. container::
+
+   .. code:: eval
+
+      CK_RV FC_Login(
+        CK_SESSION_HANDLE hSession,
+        CK_USER_TYPE userType,
+        CK_CHAR_PTR pPin,
+        CK_ULONG ulPinLen
+      );
+
+`Parameters <#parameters>`__
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. container::
+
+   ``FC_Login()`` takes four parameters:
+
+   ``hSession``
+      [in] a session handle
+   ``userType``
+      [in] the user type (``CKU_SO`` or ``CKU_USER``)
+   ``pPin``
+      [in] a pointer that points to the user's PIN
+   ``ulPinLen``
+      [in] the length of the PIN
+
+`Description <#description>`__
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. container::
+
+   ``FC_Login()`` logs a user into a token.
+
+   The Security Officer (``CKU_SO``) only logs in to initialize the normal user's PIN. The SO PIN is
+   the empty string. The NSS cryptographic module doesn't allow the SO to log in if the normal
+   user's PIN is already initialized.
+
+.. _return_value:
+
+`Return value <#return_value>`__
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. container::
+
+   ``FC_Login()`` returns the following return codes.
+
+   -  ``CKR_OK``: the user logged in successfully.
+   -  ``CKR_DEVICE_ERROR``: the token is in the Error state.
+   -  ``CKR_HOST_MEMORY``: memory allocation failed.
+   -  ``CKR_PIN_INCORRECT``: the PIN is incorrect.
+   -  ``CKR_PIN_LEN_RANGE``: the PIN is too long (``ulPinLen`` is greater than 255).
+
+      .. note::
+
+         The function should return ``CKR_PIN_INCORRECT`` in this case.
+
+   -  ``CKR_SESSION_HANDLE_INVALID``: the session handle is invalid.
+   -  ``CKR_USER_ALREADY_LOGGED_IN``: the user is already logged in.
+   -  ``CKR_USER_TYPE_INVALID``
+
+      -  The token can't authenticate the user because there is no key database or the user's
+         password isn't initialized.
+      -  ``userType`` is ``CKU_SO`` and the normal user's PIN is already initialized.
+
+.. _see_also:
+
+`See also <#see_also>`__
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. container::
+
+   -  `NSC_Login </en-US/NSC_Login>`__
+\ No newline at end of file