Pass pre encoded base64 contexts to snowplow javascript api

[agentgt]

When doing something like

snowplow('trackPageView', null, [ list,of,contexts_jsons ])

We would like to pass the contexts as a base64 instead of letting snowplow do this. That is pre generate the cx ~~variable~~ parameter.

The reasons are because generating JSON and putting that JSON on the HTML page in a script are fairly tricky due to XSS issues. Also the server is much faster at generating base64 than javascript.

Maybe this is already possible (we are using 2.6.2) in the current version but I could not find it?