diff --git a/core/server/errors/index.js b/core/server/errors/index.js
index 75205dc3d6..aaed368efb 100644
--- a/core/server/errors/index.js
+++ b/core/server/errors/index.js
@@ -245,7 +245,15 @@ errors = {
             }
             errors.renderErrorPage(err.status || 500, err, req, res, next);
         } else {
-            res.send(err.status || 500, err);
+            // generate a valid JSON response
+            var statusCode = 500,
+                errorContent = {};
+
+            statusCode = err.code || 500;
+
+            errorContent.message = _.isString(err) ? err : (_.isObject(err) ? err.message : 'Unknown Error');
+            errorContent.type = err.type || 'InternalServerError';
+            res.json(statusCode, errorContent);
         }
     }
 };
diff --git a/core/server/middleware/middleware.js b/core/server/middleware/middleware.js
index d6fb889b9c..0d6a68513d 100644
--- a/core/server/middleware/middleware.js
+++ b/core/server/middleware/middleware.js
@@ -9,11 +9,13 @@ var _           = require('lodash'),
     path        = require('path'),
     api         = require('../api'),
     passport    = require('passport'),
+    errors      = require('../errors'),
 
     expressServer,
     oauthServer,
     ONE_HOUR_MS = 60 * 60 * 1000,
-    ONE_YEAR_MS = 365 * 24 * ONE_HOUR_MS;
+    ONE_YEAR_MS = 365 * 24 * ONE_HOUR_MS,
+    loginSecurity = [];
 
 function isBlackListedFileType(file) {
     var blackListedFileTypes = ['.hbs', '.md', '.json'],
@@ -149,6 +151,31 @@ var middleware = {
         });
     },
 
+    // ### Spam prevention Middleware
+    // limit signin requests to one every two seconds
+    spamPrevention: function (req, res, next) {
+        var currentTime = process.hrtime()[0],
+            remoteAddress = req.connection.remoteAddress,
+            denied = '';
+
+        // filter for IPs that tried to login in the last 2 sec
+        loginSecurity = _.filter(loginSecurity, function (logTime) {
+            return (logTime.time + 2 > currentTime);
+        });
+
+        // check if IP tried to login in the last 2 sec
+        denied = _.find(loginSecurity, function (logTime) {
+            return (logTime.ip === remoteAddress);
+        });
+
+        if (!denied) {
+            loginSecurity.push({ip: remoteAddress, time: currentTime});
+            next();
+        } else {
+            return next(new errors.UnauthorizedError('Slow down, there are way too many login attempts!'));
+        }
+    },
+
     // work around to handle missing client_secret
     // oauth2orize needs it, but untrusted clients don't have it
     addClientSecret: function (req, res, next) {
@@ -157,9 +184,15 @@ var middleware = {
         }
         next();
     },
+
+    // ### Authenticate Client Middleware
+    // authenticate client that is asking for an access token
     authenticateClient: function (req, res, next) {
         return passport.authenticate(['oauth2-client-password'], { session: false })(req, res, next);
     },
+
+    // ### Generate access token Middleware
+    // register the oauth2orize middleware for password and refresh token grants
     generateAccessToken: function (req, res, next) {
         return oauthServer.token()(req, res, next);
     },
diff --git a/core/server/middleware/oauth.js b/core/server/middleware/oauth.js
index 5695c2257b..c97dd48d5e 100644
--- a/core/server/middleware/oauth.js
+++ b/core/server/middleware/oauth.js
@@ -43,8 +43,8 @@ oauth = {
                     }).catch(function () {
                         return done(null, false);
                     });
-                }).catch(function () {
-                    return done(null, false);
+                }).catch(function (error) {
+                    return done(error);
                 });
             });
         }));
diff --git a/core/server/models/user.js b/core/server/models/user.js
index 39585ab25a..250dd0c19c 100644
--- a/core/server/models/user.js
+++ b/core/server/models/user.js
@@ -270,15 +270,16 @@ User = ghostBookshelf.Model.extend({
         var self = this,
             s;
         return this.getByEmail(object.email).then(function (user) {
-            if (!user || user.get('status') === 'invited' || user.get('status') === 'inactive') {
-                return when.reject(new Error('NotFound'));
+            if (!user || user.get('status') === 'invited' || user.get('status') === 'invited-pending'
+                    || user.get('status') === 'inactive') {
+                return when.reject(new errors.NotFoundError('NotFound'));
             }
             if (user.get('status') !== 'locked') {
                 return nodefn.call(bcrypt.compare, object.password, user.get('password')).then(function (matched) {
                     if (!matched) {
                         return when(self.setWarning(user)).then(function (remaining) {
                             s = (remaining > 1) ? 's' : '';
-                            return when.reject(new Error('Your password is incorrect.<br>' +
+                            return when.reject(new errors.UnauthorizedError('Your password is incorrect.<br>' +
                                 remaining + ' attempt' + s + ' remaining!'));
                         });
                     }
@@ -288,7 +289,7 @@ User = ghostBookshelf.Model.extend({
                     });
                 }, errors.logAndThrowError);
             }
-            return when.reject(new Error('Your account is locked due to too many ' +
+            return when.reject(new errors.NoPermissionError('Your account is locked due to too many ' +
                 'login attempts. Please reset your password to log in again by clicking ' +
                 'the "Forgotten password?" link!'));
 
diff --git a/core/server/routes/api.js b/core/server/routes/api.js
index 07f2f88e53..4d549c5566 100644
--- a/core/server/routes/api.js
+++ b/core/server/routes/api.js
@@ -73,6 +73,7 @@ apiRoutes = function (middleware) {
     router.post('/authentication/setup', api.http(api.authentication.setup));
     router.get('/authentication/setup', api.http(api.authentication.isSetup));
     router.post('/authentication/token',
+        middleware.spamPrevention,
         middleware.addClientSecret,
         middleware.authenticateClient,
         middleware.generateAccessToken
diff --git a/core/test/functional/client/signin_test.js b/core/test/functional/client/signin_test.js
index 687263ec4f..ef6ed6b791 100644
--- a/core/test/functional/client/signin_test.js
+++ b/core/test/functional/client/signin_test.js
@@ -4,35 +4,35 @@
 /*globals CasperTest, casper, url, newUser, user, falseUser */
 
 // TODO fix signup vs setup testing
-//CasperTest.begin('Ensure a User is Registered', 3, function suite(test) {
-//    casper.thenOpenAndWaitForPageLoad('signup', function checkUrl() {
-//        test.assertUrlMatch(/ghost\/signup\/$/, 'Landed on the correct URL');
-//    });
-//
-//    casper.waitForOpaque('.signup-box',
-//        function then() {
-//            this.fillAndSave('#signup', newUser);
-//        },
-//        function onTimeout() {
-//            test.fail('Sign up form didn\'t fade in.');
-//        });
-//
-//    casper.captureScreenshot('login_register_test.png');
-//
-//    casper.waitForSelectorTextChange('.notification-error', function onSuccess() {
-//        test.assertSelectorHasText('.notification-error', 'already registered');
-//        // If the previous assert succeeds, then we should skip the next check and just pass.
-//        casper.echoConcise('Already registered!');
-//        casper.captureScreenshot('already_registered.png');
-//    }, function onTimeout() {
-//        test.assertUrlMatch(/ghost\/\d+\/$/, 'If we\'re not already registered, we should be logged in.');
-//        casper.echoConcise('Successfully registered.');
-//    }, 2000);
-//
-//    casper.thenOpenAndWaitForPageLoad('signout', function then() {
-//        test.assertUrlMatch(/ghost\/signin/, 'We got redirected to signin page.');
-//    });
-//}, true);
+CasperTest.begin('Ensure a User is Registered', 3, function suite(test) {
+   casper.thenOpenAndWaitForPageLoad('setup', function checkUrl() {
+       test.assertUrlMatch(/ghost\/setup\/$/, 'Landed on the correct URL');
+   });
+
+   casper.waitForOpaque('.setup-box',
+       function then() {
+           this.fillAndAdd('#setup', newSetup);
+       },
+       function onTimeout() {
+           test.fail('Set up form didn\'t fade in.');
+       });
+
+   casper.captureScreenshot('login_register_test.png');
+
+   casper.waitForSelectorTextChange('.notification-error', function onSuccess() {
+       test.assertSelectorHasText('.notification-error', 'already registered');
+       // If the previous assert succeeds, then we should skip the next check and just pass.
+       casper.echoConcise('Already registered!');
+       casper.captureScreenshot('already_registered.png');
+   }, function onTimeout() {
+       test.assertUrlMatch(/ghost\/\d+\/$/, 'If we\'re not already registered, we should be logged in.');
+       casper.echoConcise('Successfully registered.');
+   }, 2000);
+
+   casper.thenOpenAndWaitForPageLoad('signout', function then() {
+       test.assertUrlMatch(/ghost\/signin/, 'We got redirected to signin page.');
+   });
+}, true);
 
 CasperTest.begin('Ghost admin will load login page', 3, function suite(test) {
     casper.thenOpenAndWaitForPageLoad('signin', function testTitleAndUrl() {
@@ -59,73 +59,84 @@ CasperTest.begin('Redirects login to signin', 2, function suite(test) {
     });
 }, true);
 
-// TODO: please uncomment when the spam prevention bug is fixed (https://github.com/TryGhost/Ghost/issues/3128)
-// CasperTest.begin('Can\'t spam it', 4, function suite(test) {
-//     casper.thenOpenAndWaitForPageLoad('signin', function testTitle() {
-//         test.assertTitle('Ghost Admin', 'Ghost admin has no title');
-//         test.assertUrlMatch(/ghost\/signin\/$/, 'Landed on the correct URL');
-//     });
 
-//     casper.waitForOpaque('.login-box',
-//         function then() {
-//             this.fillAndSave('#login', falseUser);
-//         },
-//         function onTimeout() {
-//             test.fail('Sign in form didn\'t fade in.');
-//         });
+CasperTest.begin('Can\'t spam it', 4, function suite(test) {
+    // init user to prevent redirect to setup
+    CasperTest.Routines.setup.run(test);
+    CasperTest.Routines.signout.run(test);
+
+    casper.thenOpenAndWaitForPageLoad('signin', function testTitle() {
+        test.assertTitle('Ghost Admin', 'Ghost admin has no title');
+        test.assertUrlMatch(/ghost\/signin\/$/, 'Landed on the correct URL');
+    });
+
+    casper.waitForOpaque('.login-box',
+        function then() {
+            this.fillAndSave('#login', falseUser);
+        },
+        function onTimeout() {
+            test.fail('Sign in form didn\'t fade in.');
+        });
 
 
-//     casper.captureScreenshot('login_spam_test.png');
+    casper.captureScreenshot('login_spam_test.png');
 
-//     casper.waitForText('attempts remaining!', function then() {
-//         this.fillAndSave('#login', falseUser);
-//     });
+    casper.waitForText('attempts remaining!', function then() {
+        this.fillAndSave('#login', falseUser);
+    });
 
-//     casper.captureScreenshot('login_spam_test2.png');
+    casper.captureScreenshot('login_spam_test2.png');
 
-//     casper.waitForText('Slow down, there are way too many login attempts!', function onSuccess() {
-//         test.assert(true, 'Spamming the login did result in an error notification');
-//         test.assertSelectorDoesntHaveText('.notification-error', '[object Object]');
-//     }, function onTimeout() {
-//         test.assert(false, 'Spamming the login did not result in an error notification');
-//     });
+    casper.waitForText('Slow down, there are way too many login attempts!', function onSuccess() {
+        test.assert(true, 'Spamming the login did result in an error notification');
+        test.assertSelectorDoesntHaveText('.notification-error', '[object Object]');
+    }, function onTimeout() {
+        test.assert(false, 'Spamming the login did not result in an error notification');
+    });
 
-//     // This test causes the spam notification
-//     // add a wait to ensure future tests don't get tripped up by this.
-//     casper.wait(2000);
-// }, true);
+    // This test causes the spam notification
+    // add a wait to ensure future tests don't get tripped up by this.
+    casper.wait(2000);
+}, true);
 
-// TODO: please uncomment when the spam prevention bug is fixed (https://github.com/TryGhost/Ghost/issues/3128)
-// CasperTest.begin('Login limit is in place', 4, function suite(test) {
-//     casper.thenOpenAndWaitForPageLoad('signin', function testTitleAndUrl() {
-//         test.assertTitle('Ghost Admin', 'Ghost admin has no title');
-//         test.assertUrlMatch(/ghost\/signin\/$/, 'Landed on the correct URL');
-//     });
+CasperTest.begin('Login limit is in place', 4, function suite(test) {
+    // init user to prevent redirect to setup
+    CasperTest.Routines.setup.run(test);
+    CasperTest.Routines.signout.run(test);
 
-//     casper.waitForOpaque('.login-box',
-//         function then() {
-//             this.fillAndSave('#login', falseUser);
-//         },
-//         function onTimeout() {
-//             test.fail('Sign in form didn\'t fade in.');
-//         });
+    casper.thenOpenAndWaitForPageLoad('signin', function testTitleAndUrl() {
+        test.assertTitle('Ghost Admin', 'Ghost admin has no title');
+        test.assertUrlMatch(/ghost\/signin\/$/, 'Landed on the correct URL');
+    });
 
-//     casper.wait(2100, function doneWait() {
-//         this.fillAndSave('#login', falseUser);
-//     });
+    casper.waitForOpaque('.login-box',
+        function then() {
+            this.fillAndSave('#login', falseUser);
+        },
+        function onTimeout() {
+            test.fail('Sign in form didn\'t fade in.');
+        });
 
-//     casper.waitForText('remaining', function onSuccess() {
-//         test.assert(true, 'The login limit is in place.');
-//         test.assertSelectorDoesntHaveText('.notification-error', '[object Object]');
-//     }, function onTimeout() {
-//         test.assert(false, 'We did not trip the login limit.');
-//     });
-//     // This test used login, add a wait to
-//     // ensure future tests don't get tripped up by this.
-//     casper.wait(2000);
-// }, true);
+    casper.wait(2100, function doneWait() {
+        this.fillAndSave('#login', falseUser);
+    });
+
+    casper.waitForText('remaining', function onSuccess() {
+        test.assert(true, 'The login limit is in place.');
+        test.assertSelectorDoesntHaveText('.notification-error', '[object Object]');
+    }, function onTimeout() {
+        test.assert(false, 'We did not trip the login limit.');
+    });
+    // This test used login, add a wait to
+    // ensure future tests don't get tripped up by this.
+    casper.wait(2000);
+}, true);
 
 CasperTest.begin('Can login to Ghost', 5, function suite(test) {
+    // init user
+    CasperTest.Routines.setup.run(test);
+    CasperTest.Routines.signout.run(test);
+
     casper.thenOpenAndWaitForPageLoad('signin', function testTitleAndUrl() {
         test.assertTitle('Ghost Admin', 'Ghost admin has no title');
         test.assertUrlMatch(/ghost\/signin\/$/, 'Landed on the correct URL');
@@ -147,6 +158,10 @@ CasperTest.begin('Can login to Ghost', 5, function suite(test) {
 }, true);
 
 CasperTest.begin('Authenticated user is redirected', 8, function suite(test) {
+    // init user
+    CasperTest.Routines.setup.run(test);
+    CasperTest.Routines.signout.run(test);
+
     casper.thenOpenAndWaitForPageLoad('signin', function testTitleAndUrl() {
         test.assertTitle('Ghost Admin', 'Ghost admin has no title');
         test.assertUrlMatch(/ghost\/signin\/$/, 'Landed on the correct URL');
@@ -175,27 +190,31 @@ CasperTest.begin('Authenticated user is redirected', 8, function suite(test) {
     });
 }, true);
 
-// TODO: please uncomment when the validation problem is fixed (https://github.com/TryGhost/Ghost/issues/3120)
-// CasperTest.begin('Ensure email field form validation', 3, function suite(test) {
-//     casper.thenOpenAndWaitForPageLoad('signin', function testTitleAndUrl() {
-//         test.assertTitle('Ghost Admin', 'Ghost admin has no title');
-//         test.assertUrlMatch(/ghost\/signin\/$/, 'Landed on the correct URL');
-//     });
 
-//     casper.waitForOpaque('.js-login-box',
-//         function then() {
-//             this.fillAndSave('form.login-form', {
-//                 'email': 'notanemail'
-//             });
-//         },
-//         function onTimeout() {
-//             test.fail('Login form didn\'t fade in.');
-//         });
+CasperTest.begin('Ensure email field form validation', 3, function suite(test) {
+    // init user to prevent redirect to setup
+    CasperTest.Routines.setup.run(test);
+    CasperTest.Routines.signout.run(test);
 
-//     casper.waitForSelectorTextChange('.notification-error', function onSuccess() {
-//         test.assertSelectorHasText('.notification-error', 'Invalid Email');
-//     }, function onTimeout() {
-//         test.fail('Email validation error did not appear');
-//     }, 2000);
+    casper.thenOpenAndWaitForPageLoad('signin', function testTitleAndUrl() {
+        test.assertTitle('Ghost Admin', 'Ghost admin has no title');
+        test.assertUrlMatch(/ghost\/signin\/$/, 'Landed on the correct URL');
+    });
 
-// }, true);
+    casper.waitForOpaque('.js-login-box',
+        function then() {
+            this.fillAndSave('form.login-form', {
+                'identification': 'notanemail'
+            });
+        },
+        function onTimeout() {
+            test.fail('Login form didn\'t fade in.');
+        });
+
+    casper.waitForSelectorTextChange('.notification-error', function onSuccess() {
+        test.assertSelectorHasText('.notification-error', 'Invalid Email');
+    }, function onTimeout() {
+        test.fail('Email validation error did not appear');
+    }, 2000);
+
+}, true);