If you would like to use the OAuth 2 API for posting with HiveSigner server, you need to authorise the Hive account "hivesigner" to post on the behalf of your app account. Click here to do this and sign with your app account.
Finalize app account details
You can edit your app settings by updating your app account profile. Edit app settings, add avatar for your app, define redirect URIs for your OAuth2 integration. Make sure your application/website handles redirect URIs correctly.
That's it, after above steps, you should be able to write OAuth2 logics and start integrating transactions signing.