How to capture a response header and append an additional value:
In app.fastly, you will set this up under Configure–>Content–>Header
- Create a new header
’Type’ : Cache
if(beresp.http.Vary, beresp.http.Vary ", ", "") "New Value"
In the above example, if the Vary header was sent from origin, we would append
"," to it before appending the New Value . Otherwise, the header would simply have been set to New Value.