For Trigger , Views and SPs,

the default values are

SQL security = definer
and define = current_user

In some cases, it would be useful to change the default behaviour to
get more possibilities to use roles , epecially if the create statements can't be changed
later, because they are from downloaded applications etc.

So the default behaviour should be changable with system variables.

suggestion:

Variable:
definer_default

possible value:
current_user, current_role
default is current_user

For current_role , if current_role != null then back to current_user

Variable
default_sqlsecurity

possible values:
invoker, definer

default= definer