SSB Domain Auth

retrieve rpc-auth tokens from scuttlebot for web domains

example:

``js
var muxrpc = require('muxrpc')
var Serializer = require('pull-serializer')
var auth = require('ssb-domain-auth')
var chan = require('ssb-channel')

var ssb = muxrpc(ssbManifest, false, serialize)()
var localhost = chan.connect(ssb, 'localhost')

localhost.on('connect', function() {
// authenticate the connection
auth.getToken('localhost', function(err, token) {
if (err) return localhost.close(), console.error('Token fetch failed', err)
ssb.auth(token, function(err) {
if (err) return localhost.close(), console.error('Auth failed', err)

// get session info
ssb.whoami(function(err, user) {
console.log(user)
})
})
})
})

var loginBtn = document.getElementById('loginbtn')
var logoutBtn = document.getElementById('logoutbtn')

loginBtn.onclick = function(e){
e.preventDefault()
auth.openAuthPopup('localhost', {
title: '3rd-party App Auth',
perms: ['whoami'] // list of methods you want
}, function(err, granted) {
if (granted)
localhost.reconnect()
})
}
logoutBtn.onclick = function(e){
e.preventDefault()
auth.deauth('localhost')
localhost.close()
}

function serialize (stream) {
return Serializer(stream, JSON, {split: '\n\n'})
}

var ssbManifest = {
// this is just subset of the ssb api
auth: 'async',
whoami: 'async'
}
`

api:

`js
var auth = require('ssb-domain-auth')
auth.getToken(addr, cb)
auth.openAuthPopup(addr, { title: 'App Title', perms: ['list', 'of', 'rpc', 'methods' ] }, cb)
auth.deauth(addr)
auth.getAuthUrl(addr, queryStringOptsObject)
``