OpenSPP exposes an official REST API (API v2), and also supports XML-RPC for advanced/legacy integrations.
API v2 is implemented by the Odoo module spp_api_v2.
spp_api_v2
Start here:
API v2 reference
If you need direct access to Odoo models over XML-RPC (for example, for administrative scripting), see:
External API (XML-RPC)
openspp.org