Hivesigner integration

Hivesigner integration is not much different than keychain integration but it offers OAuth2 login good for mobile users as well as desktop users for unified login.

1/ Hivesigner requires app account for posting authority, @gandalf agreed and could use @hive.blog account for this.

2/ App account sign transactions either with a) hivesigner hosted API (https://hivesigner.com) or b) https://hive.blog hosted API.

• a) If hivesigner hosted API is used, @hive.blog would give posting authority for @hivesigner account and point oauth to https://hivesigner.com/api/oauth2/token

• b) If self hosted api is used e.g. https://auth.hive.blog, Hosting API is simply to run this script to handle OAuth2.

3/ One caveat is that, it will require some changes on imagehoster so user who logged in with hivesigner could also upload images. I will take responsibility for creating PR on imagehoster repo for this functionality with access_token. DONE imagehoster!1 (merged)

4/ There is SDK and demo for easy integration guide, in case of 2.b. there is setApiURL().

More info: Hivesigner Wiki