To restrict tenants for Office 365 , apply an HTTP Inspection policy:

1. Go to HTTP > HTTP Inspection > Filters.

   

2. Under the Inspection Filter section, enter a Filter Name.
3. Tick the Advanced View radio button, then copy and paste the following expression in the Patterns field:

   100278_act REQ {
   HOST: login\.microsoftonline\.com|login\.microsoft\.com|login\.windows\.net
   EVENT:
   
   { OP: HEADER_ADD HEADER: Restrict-Access-To-Tenants VALUE: your-allowed-Tenants }
   EVENT:
   
   { OP: HEADER_ADD HEADER: Restrict-Access-Context VALUE: your-allowed-Context }

    

   Replace "your-allowed-Tenants" and "your-allowed-Context" with your allowed tenants and context.
   ​
4. Go to HTTP Inspection > Policies, and make sure the newly created filter is set to Allow Scan.
5. Save and deploy the policies to the clients.