Modify "auth source" within iApp

I have been trying to "iApp" everything that I do custom on the F5 BIG-IP LTM. I know there will be somethings I can NOT do obviously, and this might be one of them, but hoping you all can help get it to work.

I want to issue the following command:

tmsh::modify auth source { 
   type active-directory
   fallback true
}        

But I keep receiving the following error:

01071762:3: The auth_source component may only be modified from the /Common folder.

I can issue the command within tmsh CLI and it will work.

tmsh modify auth source { type active-directory fallback true }

So how does one execute a command in an iApp in the /Common folder context?

Thanks!

NOTE: The "active-directory" configuration is previously being configured:

tmsh::create {  auth ldap /Common/system-auth 
    login-attribute samaccountname
    port 636
    search-base-dn dc=a***,dc=u***,dc=edu
    servers replace-all-with { *** }
    ssl enabled
    user-template %s@a****.u***.edu

}