diff --git a/Gemfile.lock b/Gemfile.lock
index 163044a..9c2e63b 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -6,7 +6,14 @@ PATH
 GEM
   remote: http://rubygems.org/
   specs:
+    bacon (1.1.0)
     diff-lcs (1.1.3)
+    em-spec (0.2.6)
+      bacon
+      eventmachine
+      rspec (> 2.6.0)
+      test-unit
+    eventmachine (0.12.10)
     rspec (2.9.0)
       rspec-core (~> 2.9.0)
       rspec-expectations (~> 2.9.0)
@@ -15,10 +22,12 @@ GEM
     rspec-expectations (2.9.1)
       diff-lcs (~> 1.1.3)
     rspec-mocks (2.9.0)
+    test-unit (2.4.4)
 
 PLATFORMS
   ruby
 
 DEPENDENCIES
+  em-spec
   rspec (~> 2.9.0)
   signature!
diff --git a/lib/signature.rb b/lib/signature.rb
index ecba0d5..6f76c77 100644
--- a/lib/signature.rb
+++ b/lib/signature.rb
@@ -110,6 +110,45 @@ def authenticate(timestamp_grace = 600)
       return token
     end
 
+    # Authenticate a request asynchronously
+    #
+    # This method is useful it you're running a server inside eventmachine and
+    # need to lookup the token asynchronously.
+    #
+    # The block is passed an auth key and a deferrable which should succeed
+    # with the token, or fail if the token cannot be found
+    #
+    # This method returns a deferrable which succeeds with the valid token, or
+    # fails with an AuthenticationError which can be used to pass the error
+    # back to the user
+    #
+    def authenticate_async(timestamp_grace = 600)
+      raise ArgumentError, "Block required" unless block_given?
+      df = EM::DefaultDeferrable.new
+
+      key = @auth_hash['auth_key']
+
+      unless key
+        df.fail(AuthenticationError.new("Missing parameter: auth_key"))
+        return
+      end
+
+      token_df = yield key
+      token_df.callback { |token|
+        begin
+          authenticate_by_token!(token, timestamp_grace)
+          df.succeed(token)
+        rescue AuthenticationError => e
+          df.fail(e)
+        end
+      }
+      token_df.errback {
+        df.fail(AuthenticationError.new("Unknown auth_key"))
+      }
+    ensure
+      return df
+    end
+
     # Expose the authentication parameters for a signed request
     #
     def auth_hash
diff --git a/signature.gemspec b/signature.gemspec
index 1f757da..3217d5c 100644
--- a/signature.gemspec
+++ b/signature.gemspec
@@ -19,4 +19,5 @@ Gem::Specification.new do |s|
 
   s.add_dependency "jruby-openssl" if defined?(JRUBY_VERSION)
   s.add_development_dependency "rspec", "~> 2.9.0"
+  s.add_development_dependency "em-spec"
 end
diff --git a/spec/signature_spec.rb b/spec/signature_spec.rb
index 35be3a4..3aa7e5f 100644
--- a/spec/signature_spec.rb
+++ b/spec/signature_spec.rb
@@ -197,5 +197,67 @@
         }.should raise_error(ArgumentError, "Block required")
       end
     end
+
+    describe "authenticate_async" do
+      include EM::SpecHelper
+      default_timeout 1
+
+      it "returns a deferrable which succeeds if authentication passes" do
+        request = Signature::Request.new('POST', '/some/path', @params)
+        em {
+          df = EM::DefaultDeferrable.new
+
+          request_df = request.authenticate_async do |key|
+            df
+          end
+
+          df.succeed(@token)
+
+          request_df.callback { |token|
+            token.should == @token
+            done
+          }
+        }
+      end
+
+      it "returns a deferrable which fails if block df fails" do
+        request = Signature::Request.new('POST', '/some/path', @params)
+        em {
+          df = EM::DefaultDeferrable.new
+
+          request_df = request.authenticate_async do |key|
+            df
+          end
+
+          df.fail()
+
+          request_df.errback { |e|
+            e.class.should == Signature::AuthenticationError
+            e.message.should == 'Unknown auth_key'
+            done
+          }
+        }
+      end
+
+      it "returns a deferrable which fails if request does not validate" do
+        request = Signature::Request.new('POST', '/some/path', @params)
+        em {
+          df = EM::DefaultDeferrable.new
+
+          request_df = request.authenticate_async do |key|
+            df
+          end
+
+          token = Signature::Token.new('key', 'wrong_secret')
+          df.succeed(token)
+
+          request_df.errback { |e|
+            e.class.should == Signature::AuthenticationError
+            e.message.should =~ /Invalid signature/
+            done
+          }
+        }
+      end
+    end
   end
 end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 0c7256c..9f61973 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -1,9 +1,8 @@
-$LOAD_PATH.unshift(File.dirname(__FILE__))
 $LOAD_PATH.unshift(File.join(File.dirname(__FILE__), '..', 'lib'))
-
-require 'rubygems'
 require 'signature'
+
 require 'rspec'
+require 'em-spec/rspec'
 
 RSpec.configure do |config|