Made some progress

app/controllers/atom_controller.rb

@@ -0,0 +1,14 @@
+class AtomController < ApplicationController
+  before_filter :set_format
+
+  def user_stream
+    @account = Account.find_by!(id: params[:id], domain: nil)
+  end
+
+  private
+
+  def set_format
+    request.format = 'xml'
+    response.headers['Content-Type'] = 'application/atom+xml'
+  end
+end

app/controllers/home_controller.rb

@@ -0,0 +1,4 @@
+class HomeController < ApplicationController
+  def index
+  end
+end

app/controllers/profile_controller.rb

@@ -0,0 +1,4 @@
+class ProfileController < ApplicationController
+  def show
+  end
+end

app/controllers/xrd_controller.rb

@@ -0,0 +1,39 @@
+class XrdController < ApplicationController
+  before_filter :set_format
+
+  def host_meta
+    @webfinger_template = "#{webfinger_url}?resource={uri}"
+  end
+
+  def webfinger
+    @account = Account.find_by!(username: username_from_resource, domain: nil)
+    @canonical_account_uri = "acct:#{@account.username}#{LOCAL_DOMAIN}"
+    @magic_key = pem_to_magic_key(@account.keypair.public_key)
+  end
+
+  private
+
+  def set_format
+    request.format = 'xml'
+    response.headers['Content-Type'] = 'application/xrd+xml'
+  end
+
+  def username_from_resource
+    params[:resource].split('@').first.gsub('acct:', '')
+  end
+
+  def pem_to_magic_key(public_key)
+    modulus, exponent = [public_key.n, public_key.e].map do |component|
+      result = ""
+
+      until component == 0 do
+        result << [component % 256].pack('C')
+        component >>= 8
+      end
+
+      result.reverse!
+    end
+
+    (["RSA"] + [modulus, exponent].map { |n| Base64.urlsafe_encode64(n) }).join('.')
+  end
+end