+#### Feedback on authentication failure reason
+
+In addition to this, in the event of an authentication failure,
+ the module exports an environment variable called MAG_ERROR wich contains one
+of the following values:
+* "NO_AUTH_DATA" when the client did not send any authentication data (usually because the
+ appropriate libraries are not installed on the browser).
+* "UNSUP_AUTH_TYPE" when the client sent authentication data of an invalid type.
+* "GSS_MECH_ERROR" when the GSS mechanism failed for some reason (e.g. invalid credentials).
+
+In addition to this, whenever MAG_ERROR takes a value of "GSS_MECH_ERROR", an additional environment
+variable named GSS_ERROR_STR is sourced. This variable contains the result of
+the gss_display_status() call and may help web developers to show a more appropriate error page/string
+to the user.
+