I haven’t done anything like this, but I think it would be a great 3PC, or extended snippet of some sort, to allow adding/editing of content to Modx remotely. (caveat: Im thinking revo here for my example, as Ive never used evo or have a clue how to do it there.)
I’d probably attempt to approach it so that:
When the ’sync’ button is pushed on your site external to modx -- curl, maybe thru through ajax, would login to your modx backend manager account (or any specific author/content editor’s backend account) so you then have permissions to create/update content. Then run a script that grabs the modx object through the API: modx object ----> the modresource object -----> ’set’ & ’setcontent’ methods. Then and use those methods to create/update your modx resources from the external php site.
Basically you’d be reusing the modx API again to control adding new (or sync’ing existing) content in the other direction. API docs here:
http://api.modxcms.com/ . Im sure there ’gottcha’s’ as far as permissions go, but someone here has certainly added external content into modx programmatically, and can detail that part of the process.