RLS when connecting 2 semantic models

For anyone who gets this issue in future, this is how i resolved it. 

1. Build a relationship between the imported table ‘Security Groups’ and your new data table (you must have a field that can be matched e.g. Project Name
2. Set the relationship so the imported table filters your data e.g. ‘Single (Security Groups filters data)
3. Create measures so you can use the security data in your RLS in this example I did 3:
   1. UserAccessLevel = CALCULATE(MAX('Security Groups'[access_level_c]),'Security Groups'[email_address] = USERPRINCIPALNAME())
   2. UserEmailMatch = IF(MAX('Security Groups'[email_address]) = USERPRINCIPALNAME(), 1, 0)
   3. UserHasProjectAccess = CALCULATE(MAX('Security Groups'[Project Name]),    'Security Groups'[email_address] = USERPRINCIPALNAME()  && 'Security Groups'[access_level_c] = "Project")
4. Go to Manage Roles, create a new role against you main table (this should be the one you linked in step 3). Switch to default editor and paste the required RLS. Below aligns with this example
   1. // Match the email to the logged-in user

'Security Groups'[UserEmailMatch] = 1

||

(

    // Allow access if the user has "Business_Unit" access

    [UserAccessLevel] = "Business_Unit"

    ||

    (

        // If the user has "Project" access, filter by matching project names

        [UserAccessLevel] = "Project"

        &&

        'TF_Transactions'[Beakon Project Name] = [UserHasProjectAccess]

    )

)