APM AdAuth HTTP Header Insert iRule Switch Statement

As Jason said, there are many ways to do this and your method looks fine.  But note your typo in IP::client_addr. And it is good practise to use -- to terminate switch options.

You could also do this by checking whether the header already exists

when ACCESS_ACL_ALLOWED
{
     if { ! [HTTP::header exists iv-user] } {
          HTTP::header insert "iv-user" [ACCESS::session data get "session.logon.last.username"] }
     }
}

Doh! My bad, thanks for that. I did find that the F5 does not like:

// do nothing

 within those braces, so I have omitted the contents and left it as:

when ACCESS_ACL_ALLOWED
{
     switch -- [IP::client_addr] {
          "10.0.0.1" -
          "10.0.0.2" {}
     default {
          HTTP::header insert "iv-user" [ACCESS::session data get "session.logon.last.username"] }
     }
}

This should be okay right?