Standard irule that can be used for multiple urls

Hello Notanf5engineer 
I've built the following bsed on given examples, it might still be incomplete and not cover all of your scenarios but it might be a good starting point 

Let me know if I can help you with improving it 

Edit: fixed syntax, tested irule 

CA

when HTTP_REQUEST {

  #If you have multiple SNI that resolve to this VS, consider enabling row below
#  if {[string tolower [HTTP::host]] ne "abcd.com"}{ return }

  switch -glob [HTTP::uri] {
    /app1/* {
	  # this will match everything starting with /app1/* (case sensitive) , remove "app1" folder and redirect 
	  # ex. /app1/test to /test 
	  # client will see the redirect

	  set uri [string trimleft [HTTP::uri] /app1]
      HTTP::redirect "http://app1.internaldomain.com/$uri"
    }
    /app2/API/hello {
	  # this is an exact match on a specific URI (case sensitive) 
	  # URI is not trimmed and is passed as-is 
	  # client will see the redirect
	  
	  HTTP::redirect "http://api2.internaldomain.com/[HTTP::uri]"
	}
	default { 
      # this matches everything not specified before
	  # HTTP::respond 401 
	}
  }
}