diff --git a/lib/omniauth/dynamic_full_host.rb b/lib/omniauth/dynamic_full_host.rb
index aeb3232..231475e 100644
--- a/lib/omniauth/dynamic_full_host.rb
+++ b/lib/omniauth/dynamic_full_host.rb
@@ -1,6 +1,6 @@
 # configures public url for our application
 module Omniauth::DynamicFullHost
-  def full_host_url(url = nil)
+  def self.full_host_url(url = nil)
     # unescapes url on-the-fly because it might be double-escaped in some environments
     #(it happens for me at work with 2 reverse-proxies in front of the app...)
     url = CGI.unescape(url) if url
@@ -10,7 +10,7 @@ def full_host_url(url = nil)
       url = Setting["host_name"]
       # else, parse it and remove both request_uri and query_string
     else
-      uri = URI.parse(URI.encode(url)) # Encode to ensure we only have ASCII charaters in url
+      uri = URI.parse(URI::Parser.new.escape(url)) # Encode to ensure we only have ASCII charaters in url
       url = "#{uri.scheme}://#{uri.host}"
       url << ":#{uri.port}" unless uri.default_port == uri.port
     end
@@ -19,5 +19,5 @@ def full_host_url(url = nil)
 end
 
 OmniAuth.config.full_host = Proc.new do |env|
-  full_host_url(env["rack.session"]["omniauth.origin"] || env["omniauth.origin"])
+  Omniauth::DynamicFullHost.full_host_url(env["rack.session"]["omniauth.origin"] || env["omniauth.origin"])
 end
diff --git a/spec/models/redmine_omniauth_cas_spec.rb b/spec/models/redmine_omniauth_cas_spec.rb
index 933a178..f89fe47 100644
--- a/spec/models/redmine_omniauth_cas_spec.rb
+++ b/spec/models/redmine_omniauth_cas_spec.rb
@@ -13,4 +13,16 @@
       expect(RedmineOmniauthCas.cas_service_validate_url).to be_nil
     end
   end
+
+  context "dynamic full host" do
+    it "should return host name from setting if no url" do
+      Setting["host_name"] = "http://redmine.example.com"
+      expect(Omniauth::DynamicFullHost.full_host_url).to eq "http://redmine.example.com"
+    end
+
+    it "should return host name from url if url is present" do
+      url = "https://redmine.example.com:3000/some/path"
+      expect(Omniauth::DynamicFullHost.full_host_url(url)).to eq "https://redmine.example.com:3000"
+    end
+  end
 end