SCHEDD.SEC_WRITE_AUTHENTICATION_METHODS = FS,TOKEN,SCITOKENS,SSL,GSI
   SCHEDD.SEC_READ_AUTHENTICATION_METHODS = FS,TOKEN,SCITOKENS,SSL,GSI
+  SCHEDD.AUTH_SSL_REQUIRE_CLIENT_CERTIFICATE = True
 
 6. Once all of the peers of a given client or CE are authenticating
 successfully via SSL, you can upgrade to HTCondor-CE 6 and HTCondor 10.X.