erp5_oauth_authorisation: Improve readability in a few places

No functional change expected.
6 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
failed ERP5.CodingStyleTest-Master

01:07:59

passed ERP5.PerformanceTest-Master

00:25:54

failed ERP5.UnitTest-Master

01:27:32

failed ERP5.UnitTest-Master.Medusa

01:36:08

passed SlapOS.Eggs.UnitTest-Master.Python2

00:12:28

passed SlapOS.Eggs.UnitTest-Master.Python3

00:13:54