diff --git a/docs/porting-guide.rst b/docs/porting-guide.rst
index 7a3963b..c3df389 100644
--- a/docs/porting-guide.rst
+++ b/docs/porting-guide.rst
@@ -1792,6 +1792,22 @@
 On DynamIQ systems, this function must not use stack while enabling MMU, which
 is how the function in xlat table library version 2 is implemented.
 
+Function : plat_init_apiakey [optional]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+::
+
+    Argument : void
+    Return   : uint64_t *
+
+This function populates the ``plat_apiakey`` array that contains the values used
+to set the ``APIAKey{Hi,Lo}_EL1`` registers. It returns a pointer to this array.
+
+The value should be obtained from a reliable source of randomness.
+
+This function is only needed if ARMv8.3 pointer authentication is used in the
+Trusted Firmware by building with ``ENABLE_PAUTH=1``.
+
 Function : plat_get_syscnt_freq2() [mandatory]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~