This page is just a reference of all the known Steam APIs, I do not know how they work. Please do not email me with questions.
GETGetEquippedPlayerItems
https://api.steampowered.com/IEconItems_583950/GetEquippedPlayerItems/v1/
NameValueTypeRequiredDescription
uint64 Yes The Steam ID to fetch items for
uint32 Yes Return items equipped for this class id