Please try the following patch and let us know if it resolves the
output token buffer leak.

Index: src/lib/gssapi/spnego/spnego_mech.c
===================================================================
--- src/lib/gssapi/spnego/spnego_mech.c	(revision 19756)
+++ src/lib/gssapi/spnego/spnego_mech.c	(revision 19757)
@@ -835,6 +835,7 @@
 			ret = GSS_S_FAILURE;
 		}
 	}
+	gss_release_buffer(tmpmin, &mechtok_out);
 	if (ret == GSS_S_COMPLETE) {
 		/*
 		 * Now, switch the output context to refer to the