diff --git a/keystone.lisp b/keystone.lisp
index 2b16c3f..61fba75 100644
--- a/keystone.lisp
+++ b/keystone.lisp
@@ -17,12 +17,41 @@
 
 
 (defclass connection ()
-  ((username :initarg :username :reader connection-username)
-   (tenant-id :initarg :tenant-id :initform nil :reader connection-tenant-id)
-   (tenant-name :initarg :tenant-name :initform nil :reader connection-tenant-name)
-   (password :initarg :password :reader connection-password)
+  ((username :initarg :username
+             :reader connection-username
+             :initform (error ":USERNAME is required when creating a connection."))
+   (tenant-id :initarg :tenant-id
+              :reader connection-tenant-id)
+   (tenant-name :initarg :tenant-name
+                :reader connection-tenant-name)
+   (password :initarg :password
+             :initform (error ":PASSWORD is required when creating a connection.")
+             :reader connection-password)
    (token :initarg :password)
-   (url :initarg :url :reader connection-url)))
+   (url :initarg :url
+        :reader connection-url
+        :initform (error ":URL is required when creating a connection."))))
+
+(defmethod encode-json ((connection connection)
+                        &optional (stream json:*json-output*))
+  "Write the JSON representation (Object) of the keystone CONNECTION
+to STREAM (or to *JSON-OUTPUT*)."
+  (with-slots (username password) connection
+    (with-explicit-encoder
+      (encode-json
+       `(:object
+         :auth
+         (:object
+          :password-credentials
+          (:object
+           :username ,username
+           :password ,password)
+          ,@(cond
+              ((slot-boundp connection 'tenant-id)
+               (list :tenant-id (connection-tenant-id connection)))
+              ((slot-boundp connection 'tenant-name)
+               (list :tenant-name (connection-tenant-name connection))))))
+       stream))))
 
 (defclass connection-v2 (connection)
   ((version :initform 2 :reader connection-version)))
@@ -66,35 +95,25 @@
   (:documentation "Authenticate and retrieve a token."))
 
 (defmethod authenticate ((connection connection-v2))
-  (with-slots (url token username password tenant-id tenant-name) connection
-    (unless (or tenant-id tenant-name)
-      (error "No tenant-id nor tenant-name specified, cannot authenticate."))
-    (let ((tenant-prop (if tenant-id
-                           (list "tenantId" tenant-id)
-                           (list "tenantName" tenant-name))))
-      (multiple-value-bind (body status-code headers uri stream must-close reason-phrase)
-          (http-request (format nil "~a/v2.0/tokens" url)
-                        :method :POST
-                        :want-stream t
-                        :stream *cached-stream*
-                        :content-type "application/json"
-                        :content
-                        (with-explicit-encoder
-                          (encode-json-to-string
-                           `(:object "auth" (:object "passwordCredentials"
-                                                     (:object "username" ,username
-                                                              "password" ,password)
-                                                     ,@tenant-prop)))))
-        (declare (ignore must-close reason-phrase body))
-        (cond
-          ((and (eql status-code 200)
-                (json-response-p headers))
-           (setf token
-                 (cdr (assoc :token (cdr (assoc :access (decode-json stream)))))))
-          ((json-response-p headers)
-           (json-error (decode-json stream)))
-          (t
-           (unknown-error uri status-code)))))))
+  (with-slots (url token) connection
+    (multiple-value-bind (body status-code headers uri stream must-close reason-phrase)
+        (http-request (format nil "~a/v2.0/tokens" url)
+                      :method :POST
+                      :want-stream t
+                      :stream *cached-stream*
+                      :content-type "application/json"
+                      :content
+                      (encode-json-to-string connection))
+      (declare (ignore must-close reason-phrase body))
+      (cond
+        ((and (eql status-code 200)
+              (json-response-p headers))
+         (setf token
+               (cdr (assoc :token (cdr (assoc :access (decode-json stream)))))))
+        ((json-response-p headers)
+         (json-error (decode-json stream)))
+        (t
+         (unknown-error uri status-code))))))
 
 (defgeneric connection-token-id (connection)
   (:documentation "Retrieve token id for CONNECTION."))
diff --git a/tests/keystone.lisp b/tests/keystone.lisp
index ad7051d..326f7ce 100644
--- a/tests/keystone.lisp
+++ b/tests/keystone.lisp
@@ -17,7 +17,7 @@
 
 (in-package :cl-keystone-client-test)
 
-(def-suite keystone :description "My Example Suite")
+(def-suite keystone :description "Test the Openstack Keystone client.")
 
 (in-suite keystone)
 
@@ -54,8 +54,24 @@
                             (coerce '(#\Return #\Linefeed) 'string)))))
 
 (test make-connection
-      "Make a connection object"
-      (is-true (make-instance 'connection-v2)))
+  "Make a connection testing required fields."
+  (is-true
+   (make-instance 'connection-v2
+                  :username "test"
+                  :password "test"
+                  :url "test"))
+  (signals error
+    (make-instance 'connection-v2
+                   :password "test"
+                   :url "test"))
+  (signals error
+    (make-instance 'connection-v2
+                   :username "test"
+                   :url "test"))
+  (signals error
+    (make-instance 'connection-v2
+                   :username "test"
+                   :password "test")))
 
 (test authentication-error-404
   "Test that the correct condition is signalled when a 404 is returned