allowed  preflight  response  | text |
   -------  ---------  --------  | ---- |
 1      no          x       400  |   no |
 2      no        200         x  |   no |
 3     yes          x       200  |  yes |
 4     yes          x       400  |  yes |
 5     yes        200       200  |  yes |
 6     yes        200       400  |  yes |
 7     yes        400         x  |   no |