"Support paid apps by means of an authorization model that uses existing identity systems like OpenID." I like the idea of this. I wish it was easier to sell

"Support paid apps by means of an authorization model that uses existing identity systems like OpenID." I like the idea of this. I wish it was easier to sell the web apps I build, in a way that's as easy as plugging in OpenID. I've looked at a few services that promise this but they either need US a merchant account or something else I don't have/can't get.