Doc: Update link to TBBR-CLIENT specification

Change-Id: Iafa79b6f7891d3eebec9908a8f7725131202beb3
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>
diff --git a/docs/auth-framework.rst b/docs/auth-framework.rst
index 317ac18..0142fbd 100644
--- a/docs/auth-framework.rst
+++ b/docs/auth-framework.rst
@@ -80,7 +80,7 @@
 A CoT is basically a sequence of authentication images which usually starts with
 a root of trust and culminates in a single data image. The following diagram
 illustrates how this maps to a CoT for the BL31 image described in the
-TBBR-Client specification.
+`TBBR-Client specification`_.
 
 ::
 
@@ -969,3 +969,4 @@
 
 .. _Trusted Board Boot: ./trusted-board-boot.rst
 .. _Platform Porting Guide: ./porting-guide.rst
+.. _TBBR-Client specification: https://developer.arm.com/docs/den0006/latest/trusted-board-boot-requirements-client-tbbr-client-armv8-a