diff --git a/composer.json b/composer.json
index 804cdc3b..9efabab0 100644
--- a/composer.json
+++ b/composer.json
@@ -2,7 +2,7 @@
     "name": "imsglobal/lti-1p3-tool",
     "type": "library",
     "require": {
-        "fproject/php-jwt": "^4.0",
+        "firebase/php-jwt": "^5.2",
         "phpseclib/phpseclib": "^2.0"
     },
     "autoload": {
diff --git a/src/lti/Cache.php b/src/lti/Cache.php
index 0d865711..f8c13c4b 100644
--- a/src/lti/Cache.php
+++ b/src/lti/Cache.php
@@ -1,46 +1,9 @@
 <?php
 namespace IMSGlobal\LTI;
 
-class Cache {
-
-    private $cache;
-
-    public function get_launch_data($key) {
-        $this->load_cache();
-        return $this->cache[$key];
-    }
-
-    public function cache_launch_data($key, $jwt_body) {
-        $this->cache[$key] = $jwt_body;
-        $this->save_cache();
-        return $this;
-    }
-
-    public function cache_nonce($nonce) {
-        $this->cache['nonce'][$nonce] = true;
-        $this->save_cache();
-        return $this;
-    }
-
-    public function check_nonce($nonce) {
-        $this->load_cache();
-        if (!isset($this->cache['nonce'][$nonce])) {
-            return false;
-        }
-        return true;
-    }
-
-    private function load_cache() {
-        $cache = file_get_contents(sys_get_temp_dir() . '/lti_cache.txt');
-        if (empty($cache)) {
-            file_put_contents(sys_get_temp_dir() . '/lti_cache.txt', '{}');
-            $this->cache = [];
-        }
-        $this->cache = json_decode($cache, true);
-    }
-
-    private function save_cache() {
-        file_put_contents(sys_get_temp_dir() . '/lti_cache.txt', json_encode($this->cache));
-    }
+interface Cache {
+    public function get_launch_data($key);
+    public function cache_launch_data($key, $jwt_body);
+    public function cache_nonce($nonce);
+    public function check_nonce($nonce);
 }
-?>
\ No newline at end of file
diff --git a/src/lti/Cookie.php b/src/lti/Cookie.php
index e18700b6..1d588fec 100644
--- a/src/lti/Cookie.php
+++ b/src/lti/Cookie.php
@@ -1,34 +1,7 @@
 <?php
 namespace IMSGlobal\LTI;
 
-class Cookie {
-    public function get_cookie($name) {
-        if (isset($_COOKIE[$name])) {
-            return $_COOKIE[$name];
-        }
-        // Look for backup cookie if same site is not supported by the user's browser.
-        if (isset($_COOKIE["LEGACY_" . $name])) {
-            return $_COOKIE["LEGACY_" . $name];
-        }
-        return false;
-    }
-
-    public function set_cookie($name, $value, $exp = 3600, $options = []) {
-        $cookie_options = [
-            'expires' => time() + $exp
-        ];
-
-        // SameSite none and secure will be required for tools to work inside iframes
-        $same_site_options = [
-            'samesite' => 'None',
-            'secure' => true
-        ];
-
-        setcookie($name, $value, array_merge($cookie_options, $same_site_options, $options));
-
-        // Set a second fallback cookie in the event that "SameSite" is not supported
-        setcookie("LEGACY_" . $name, $value, array_merge($cookie_options, $options));
-        return $this;
-    }
+interface Cookie {
+    public function get_cookie($name);
+    public function set_cookie($name, $value, $exp = 3600, $options = []);
 }
-?>
diff --git a/src/lti/Database.php b/src/lti/Database.php
index 945afd67..d002fef8 100644
--- a/src/lti/Database.php
+++ b/src/lti/Database.php
@@ -6,4 +6,3 @@ public function find_registration_by_issuer($iss);
     public function find_deployment($iss, $deployment_id);
 }
 
-?>
\ No newline at end of file
diff --git a/src/lti/ImsCache.php b/src/lti/ImsCache.php
new file mode 100644
index 00000000..b52f71f5
--- /dev/null
+++ b/src/lti/ImsCache.php
@@ -0,0 +1,45 @@
+<?php
+namespace IMSGlobal\LTI;
+
+class ImsCache {
+
+    private $cache;
+
+    public function get_launch_data($key) {
+        $this->load_cache();
+        return $this->cache[$key];
+    }
+
+    public function cache_launch_data($key, $jwt_body) {
+        $this->cache[$key] = $jwt_body;
+        $this->save_cache();
+        return $this;
+    }
+
+    public function cache_nonce($nonce) {
+        $this->cache['nonce'][$nonce] = true;
+        $this->save_cache();
+        return $this;
+    }
+
+    public function check_nonce($nonce) {
+        $this->load_cache();
+        if (!isset($this->cache['nonce'][$nonce])) {
+            return false;
+        }
+        return true;
+    }
+
+    private function load_cache() {
+        $cache = file_get_contents(sys_get_temp_dir() . '/lti_cache.txt');
+        if (empty($cache)) {
+            file_put_contents(sys_get_temp_dir() . '/lti_cache.txt', '{}');
+            $this->cache = [];
+        }
+        $this->cache = json_decode($cache, true);
+    }
+
+    private function save_cache() {
+        file_put_contents(sys_get_temp_dir() . '/lti_cache.txt', json_encode($this->cache));
+    }
+}
diff --git a/src/lti/ImsCookie.php b/src/lti/ImsCookie.php
new file mode 100644
index 00000000..ee1feb35
--- /dev/null
+++ b/src/lti/ImsCookie.php
@@ -0,0 +1,33 @@
+<?php
+namespace IMSGlobal\LTI;
+
+class ImsCookie {
+    public function get_cookie($name) {
+        if (isset($_COOKIE[$name])) {
+            return $_COOKIE[$name];
+        }
+        // Look for backup cookie if same site is not supported by the user's browser.
+        if (isset($_COOKIE["LEGACY_" . $name])) {
+            return $_COOKIE["LEGACY_" . $name];
+        }
+        return false;
+    }
+
+    public function set_cookie($name, $value, $exp = 3600, $options = []) {
+        $cookie_options = [
+            'expires' => time() + $exp
+        ];
+
+        // SameSite none and secure will be required for tools to work inside iframes
+        $same_site_options = [
+            'samesite' => 'None',
+            'secure' => true
+        ];
+
+        setcookie($name, $value, array_merge($cookie_options, $same_site_options, $options));
+
+        // Set a second fallback cookie in the event that "SameSite" is not supported
+        setcookie("LEGACY_" . $name, $value, array_merge($cookie_options, $options));
+        return $this;
+    }
+}
diff --git a/src/lti/LTI_Assignments_Grades_Service.php b/src/lti/LTI_Assignments_Grades_Service.php
index ffd1cde0..816c8757 100644
--- a/src/lti/LTI_Assignments_Grades_Service.php
+++ b/src/lti/LTI_Assignments_Grades_Service.php
@@ -12,7 +12,7 @@ public function __construct(LTI_Service_Connector $service_connector, $service_d
     }
 
     public function put_grade(LTI_Grade $grade, LTI_Lineitem $lineitem = null) {
-        if (!in_array("https://purl.imsglobal.org/spec/lti-ags/scope/score", $this->service_data['scope'])) {
+        if (!in_array(LTI_Constants::AGS_SCORE, $this->service_data['scope'])) {
             throw new LTI_Exception('Missing required scope', 1);
         }
         $score_url = '';
@@ -42,7 +42,7 @@ public function put_grade(LTI_Grade $grade, LTI_Lineitem $lineitem = null) {
     }
 
     public function find_or_create_lineitem(LTI_Lineitem $new_line_item) {
-        if (!in_array("https://purl.imsglobal.org/spec/lti-ags/scope/lineitem", $this->service_data['scope'])) {
+        if (!in_array(LTI_Constants::AGS_LINEITEM, $this->service_data['scope'])) {
             throw new LTI_Exception('Missing required scope', 1);
         }
         $line_items = $this->service_connector->make_service_request(
@@ -88,4 +88,3 @@ public function get_grades(LTI_Lineitem $lineitem) {
         return $scores['body'];
     }
 }
-?>
\ No newline at end of file
diff --git a/src/lti/LTI_Constants.php b/src/lti/LTI_Constants.php
new file mode 100644
index 00000000..80703cdf
--- /dev/null
+++ b/src/lti/LTI_Constants.php
@@ -0,0 +1,77 @@
+<?php
+
+namespace IMSGlobal\LTI;
+
+class LTI_Constants
+{
+    public const V1_3 = '1.3.0';
+
+    // Required message claims
+    public const MESSAGE_TYPE = 'https://purl.imsglobal.org/spec/lti/claim/message_type';
+    public const VERSION = 'https://purl.imsglobal.org/spec/lti/claim/version';
+    public const DEPLOYMENT_ID = 'https://purl.imsglobal.org/spec/lti/claim/deployment_id';
+    public const TARGET_LINK_URI = 'https://purl.imsglobal.org/spec/lti/claim/target_link_uri';
+    public const RESOURCE_LINK = 'https://purl.imsglobal.org/spec/lti/claim/resource_link';
+    public const ROLES = 'https://purl.imsglobal.org/spec/lti/claim/roles';
+
+    // Optional message claims
+    public const CONTEXT = 'https://purl.imsglobal.org/spec/lti/claim/context';
+    public const TOOL_PLATFORM = 'https://purl.imsglobal.org/spec/lti/claim/tool_platform';
+    public const ROLE_SCOPE_MENTOR = 'https://purlimsglobal.org/spec/lti/claim/role_scope_mentor';
+    public const LAUNCH_PRESENTATION = 'https://purl.imsglobal.org/spec/lti/claim/launch_presentation';
+    public const LIS = 'https://purl.imsglobal.org/spec/lti/claim/lis';
+    public const CUSTOM = 'https://purl.imsglobal.org/spec/lti/claim/custom';
+
+    // LTI DL
+    public const DL_CONTENT_ITEMS = 'https://purl.imsglobal.org/spec/lti-dl/claim/content_items';
+    public const DL_DATA = 'https://purl.imsglobal.org/spec/lti-dl/claim/data';
+    public const DL_DEEP_LINK_SETTINGS = 'https://purl.imsglobal.org/spec/lti-dl/claim/deep_linking_settings';
+
+    // LTI NRPS
+    public const NRPS_CLAIM_SERVICE = 'https://purl.imsglobal.org/spec/lti-nrps/claim/namesroleservice';
+    public const NRPS_SCOPE_MEMBERSHIP_READONLY = 'https://purl.imsglobal.org/spec/lti-nrps/scope/contextmembership.readonly';
+
+    // LTI AGS
+    public const AGS_CLAIM_ENDPOINT = 'https://purl.imsglobal.org/spec/lti-ags/claim/endpoint';
+    public const AGS_SCOPE_LINEITEM = 'https://purl.imsglobal.org/spec/lti-ags/scope/lineitem';
+    public const AGS_SCOPE_LINEITEM_READONLY = 'https://purl.imsglobal.org/spec/lti-ags/scope/lineitem.readonly';
+    public const AGS_SCOPE_RESULT_READONLY = 'https://purl.imsglobal.org/spec/lti-ags/scope/result.readonly';
+    public const AGS_SCOPE_SCORE = 'https://purl.imsglobal.org/spec/lti-ags/scope/score';
+
+    // User Vocab
+    public const SYSTEM_ADMINISTRATOR = 'http://purl.imsglobal.org/vocab/lis/v2/system/person#Administrator';
+    public const SYSTEM_NONE = 'http://purl.imsglobal.org/vocab/lis/v2/system/person#None';
+    public const SYSTEM_ACCOUNTADMIN = 'http://purl.imsglobal.org/vocab/lis/v2/system/person#AccountAdmin';
+    public const SYSTEM_CREATOR = 'http://purl.imsglobal.org/vocab/lis/v2/system/person#Creator';
+    public const SYSTEM_SYSADMIN = 'http://purl.imsglobal.org/vocab/lis/v2/system/person#SysAdmin';
+    public const SYSTEM_SYSSUPPORT = 'http://purl.imsglobal.org/vocab/lis/v2/system/person#SysSupport';
+    public const SYSTEM_USER = 'http://purl.imsglobal.org/vocab/lis/v2/system/person#User';
+    public const INSTITUTION_ADMINISTRATOR = 'http://purl.imsglobal.org/vocab/lis/v2/institution/person#Administrator';
+    public const INSTITUTION_FACULTY = 'http://purl.imsglobal.org/vocab/lis/v2/institution/person#Faculty';
+    public const INSTITUTION_GUEST = 'http://purl.imsglobal.org/vocab/lis/v2/institution/person#Guest';
+    public const INSTITUTION_NONE = 'http://purl.imsglobal.org/vocab/lis/v2/institution/person#None';
+    public const INSTITUTION_OTHER = 'http://purl.imsglobal.org/vocab/lis/v2/institution/person#Other';
+    public const INSTITUTION_STAFF = 'http://purl.imsglobal.org/vocab/lis/v2/institution/person#Staff';
+    public const INSTITUTION_STUDENT = 'http://purl.imsglobal.org/vocab/lis/v2/institution/person#Student';
+    public const INSTITUTION_ALUMNI = 'http://purl.imsglobal.org/vocab/lis/v2/institution/person#Alumni';
+    public const INSTITUTION_INSTRUCTOR = 'http://purl.imsglobal.org/vocab/lis/v2/institution/person#Instructor';
+    public const INSTITUTION_LEARNER = 'http://purl.imsglobal.org/vocab/lis/v2/institution/person#Learner';
+    public const INSTITUTION_MEMBER = 'http://purl.imsglobal.org/vocab/lis/v2/institution/person#Member';
+    public const INSTITUTION_MENTOR = 'http://purl.imsglobal.org/vocab/lis/v2/institution/person#Mentor';
+    public const INSTITUTION_OBSERVER = 'http://purl.imsglobal.org/vocab/lis/v2/institution/person#Observer';
+    public const INSTITUTION_PROSPECTIVESTUDENT = 'http://purl.imsglobal.org/vocab/lis/v2/institution/person#ProspectiveStudent';
+    public const MEMBERSHIP_ADMINISTRATOR = 'http://purl.imsglobal.org/vocab/lis/v2/membership#Administrator';
+    public const MEMBERSHIP_CONTENTDEVELOPER = 'http://purl.imsglobal.org/vocab/lis/v2/membership#ContentDeveloper';
+    public const MEMBERSHIP_INSTRUCTOR = 'http://purl.imsglobal.org/vocab/lis/v2/membership#Instructor';
+    public const MEMBERSHIP_LEARNER = 'http://purl.imsglobal.org/vocab/lis/v2/membership#Learner';
+    public const MEMBERSHIP_MENTOR = 'http://purl.imsglobal.org/vocab/lis/v2/membership#Mentor';
+    public const MEMBERSHIP_MANAGER = 'http://purl.imsglobal.org/vocab/lis/v2/membership#Manager';
+    public const MEMBERSHIP_MEMBER = 'http://purl.imsglobal.org/vocab/lis/v2/membership#Member';
+    public const MEMBERSHIP_OFFICER = 'http://purl.imsglobal.org/vocab/lis/v2/membership#Officer';
+
+    // Context Vocab
+    public const COURSE_TEMPLATE = 'http://purl.imsglobal.org/vocab/lis/v2/course#CourseTemplate';
+    public const COURSE_OFFERING = 'http://purl.imsglobal.org/vocab/lis/v2/course#CourseOffering';
+    public const COURSE_SECTION = 'http://purl.imsglobal.org/vocab/lis/v2/course#CourseSection';
+    public const COURSE_GROUP = 'http://purl.imsglobal.org/vocab/lis/v2/course#Group';
+}
diff --git a/src/lti/LTI_Deep_Link.php b/src/lti/LTI_Deep_Link.php
index c87cb0da..69362d09 100644
--- a/src/lti/LTI_Deep_Link.php
+++ b/src/lti/LTI_Deep_Link.php
@@ -21,11 +21,11 @@ public function get_response_jwt($resources) {
             "exp" => time() + 600,
             "iat" => time(),
             "nonce" => 'nonce' . hash('sha256', random_bytes(64)),
-            "https://purl.imsglobal.org/spec/lti/claim/deployment_id" => $this->deployment_id,
-            "https://purl.imsglobal.org/spec/lti/claim/message_type" => "LtiDeepLinkingResponse",
-            "https://purl.imsglobal.org/spec/lti/claim/version" => "1.3.0",
-            "https://purl.imsglobal.org/spec/lti-dl/claim/content_items" => array_map(function($resource) { return $resource->to_array(); }, $resources),
-            "https://purl.imsglobal.org/spec/lti-dl/claim/data" => $this->deep_link_settings['data'],
+            LTI_Constants::DEPLOYMENT_ID => $this->deployment_id,
+            LTI_Constants::MESSAGE_TYPE => "LtiDeepLinkingResponse",
+            LTI_Constants::VERSION => LTI_Constants::V1_3,
+            LTI_Constants::DL_CONTENT_ITEMS => array_map(function($resource) { return $resource->to_array(); }, $resources),
+            LTI_Constants::DL_DATA => $this->deep_link_settings['data'],
         ];
         return JWT::encode($message_jwt, $this->registration->get_tool_private_key(), 'RS256', $this->registration->get_kid());
     }
@@ -43,4 +43,3 @@ public function output_response_form($resources) {
         <?php
     }
 }
-?>
\ No newline at end of file
diff --git a/src/lti/LTI_Deep_Link_Resource.php b/src/lti/LTI_Deep_Link_Resource.php
index 8abeadd6..7b1d97ce 100644
--- a/src/lti/LTI_Deep_Link_Resource.php
+++ b/src/lti/LTI_Deep_Link_Resource.php
@@ -87,4 +87,4 @@ public function to_array() {
         return $resource;
     }
 }
-?>
+
diff --git a/src/lti/LTI_Deployment.php b/src/lti/LTI_Deployment.php
index ad502055..2b823831 100644
--- a/src/lti/LTI_Deployment.php
+++ b/src/lti/LTI_Deployment.php
@@ -20,4 +20,3 @@ public function set_deployment_id($deployment_id) {
 
 }
 
-?>
\ No newline at end of file
diff --git a/src/lti/LTI_Exception.php b/src/lti/LTI_Exception.php
index b54bf7d3..8cd9f27e 100644
--- a/src/lti/LTI_Exception.php
+++ b/src/lti/LTI_Exception.php
@@ -4,4 +4,3 @@
 class LTI_Exception extends \Exception {
 
 }
-?>
\ No newline at end of file
diff --git a/src/lti/LTI_Grade.php b/src/lti/LTI_Grade.php
index fabeb6ad..e256bcd0 100644
--- a/src/lti/LTI_Grade.php
+++ b/src/lti/LTI_Grade.php
@@ -103,4 +103,3 @@ public function __toString() {
         ]));
     }
 }
-?>
\ No newline at end of file
diff --git a/src/lti/LTI_Lineitem.php b/src/lti/LTI_Lineitem.php
index ba8e20a7..3b01269b 100644
--- a/src/lti/LTI_Lineitem.php
+++ b/src/lti/LTI_Lineitem.php
@@ -105,4 +105,3 @@ public function __toString() {
         ]));
     }
 }
-?>
\ No newline at end of file
diff --git a/src/lti/LTI_Message_Launch.php b/src/lti/LTI_Message_Launch.php
index 7a18195d..9bb7cebc 100644
--- a/src/lti/LTI_Message_Launch.php
+++ b/src/lti/LTI_Message_Launch.php
@@ -3,6 +3,7 @@
 
 use Firebase\JWT\JWK;
 use Firebase\JWT\JWT;
+use Firebase\JWT\ExpiredException;
 
 JWT::$leeway = 5;
 
@@ -29,12 +30,12 @@ function __construct(Database $database, Cache $cache = null, Cookie $cookie = n
         $this->launch_id = uniqid("lti1p3_launch_", true);
 
         if ($cache === null) {
-            $cache = new Cache();
+            $cache = new ImsCache();
         }
         $this->cache = $cache;
 
         if ($cookie === null) {
-            $cookie = new Cookie();
+            $cookie = new ImsCookie();
         }
         $this->cookie = $cookie;
     }
@@ -94,7 +95,7 @@ public function validate(array $request = null) {
      * @return boolean  Returns a boolean indicating the availability of names and roles.
      */
     public function has_nrps() {
-        return !empty($this->jwt['body']['https://purl.imsglobal.org/spec/lti-nrps/claim/namesroleservice']['context_memberships_url']);
+        return !empty($this->jwt['body'][LTI_Constants::NRPS_NAMESROLESPROVISIONINGSERVICE]['context_memberships_url']);
     }
 
     /**
@@ -105,7 +106,7 @@ public function has_nrps() {
     public function get_nrps() {
         return new LTI_Names_Roles_Provisioning_Service(
             new LTI_Service_Connector($this->registration),
-            $this->jwt['body']['https://purl.imsglobal.org/spec/lti-nrps/claim/namesroleservice']);
+            $this->jwt['body'][LTI_Constants::NRPS_NAMESROLESPROVISIONINGSERVICE]);
     }
 
     /**
@@ -134,7 +135,7 @@ public function get_gs() {
      * @return boolean  Returns a boolean indicating the availability of assignments and grades.
      */
     public function has_ags() {
-        return !empty($this->jwt['body']['https://purl.imsglobal.org/spec/lti-ags/claim/endpoint']);
+        return !empty($this->jwt['body'][LTI_Constants::AGS_ENDPOINT]);
     }
 
     /**
@@ -145,7 +146,7 @@ public function has_ags() {
     public function get_ags() {
         return new LTI_Assignments_Grades_Service(
             new LTI_Service_Connector($this->registration),
-            $this->jwt['body']['https://purl.imsglobal.org/spec/lti-ags/claim/endpoint']);
+            $this->jwt['body'][LTI_Constants::AGS_ENDPOINT]);
     }
 
     /**
@@ -156,8 +157,8 @@ public function get_ags() {
     public function get_deep_link() {
         return new LTI_Deep_Link(
             $this->registration,
-            $this->jwt['body']['https://purl.imsglobal.org/spec/lti/claim/deployment_id'],
-            $this->jwt['body']['https://purl.imsglobal.org/spec/lti-dl/claim/deep_linking_settings']);
+            $this->jwt['body'][LTI_Constants::DEPLOYMENT_ID],
+            $this->jwt['body'][LTI_Constants::DL_DEEP_LINK_SETTINGS]);
     }
 
     /**
@@ -166,7 +167,7 @@ public function get_deep_link() {
      * @return boolean  Returns true if the current launch is a deep linking launch.
      */
     public function is_deep_link_launch() {
-        return $this->jwt['body']['https://purl.imsglobal.org/spec/lti/claim/message_type'] === 'LtiDeepLinkingRequest';
+        return $this->jwt['body'][LTI_Constants::MESSAGE_TYPE] === 'LtiDeepLinkingRequest';
     }
 
     /**
@@ -184,7 +185,7 @@ public function is_submission_review_launch() {
      * @return boolean  Returns true if the current launch is a resource launch.
      */
     public function is_resource_launch() {
-        return $this->jwt['body']['https://purl.imsglobal.org/spec/lti/claim/message_type'] === 'LtiResourceLinkRequest';
+        return $this->jwt['body'][LTI_Constants::MESSAGE_TYPE] === 'LtiResourceLinkRequest';
     }
 
     /**
@@ -220,7 +221,11 @@ private function get_public_key() {
         foreach ($public_key_set['keys'] as $key) {
             if ($key['kid'] == $this->jwt['header']['kid']) {
                 try {
-                    return openssl_pkey_get_details(JWK::parseKey($key));
+                    return openssl_pkey_get_details(
+                        JWK::parseKeySet([
+                            'keys' => [$key]
+                        ])[$key['kid']]
+                    );
                 } catch(\Exception $e) {
                     return false;
                 }
@@ -269,6 +274,9 @@ private function validate_jwt_format() {
     }
 
     private function validate_nonce() {
+        if (!isset($this->jwt['body']['nonce'])) {
+            throw new LTI_Exception("Missing Nonce");
+        }
         if (!$this->cache->check_nonce($this->jwt['body']['nonce'])) {
             //throw new LTI_Exception("Invalid Nonce");
         }
@@ -294,14 +302,17 @@ private function validate_registration() {
     }
 
     private function validate_jwt_signature() {
+        if (!isset($this->jwt['header']['kid'])) {
+            throw new LTI_Exception("No KID specified in the JWT Header");
+        }
+
         // Fetch public key.
         $public_key = $this->get_public_key();
 
         // Validate JWT signature
         try {
             JWT::decode($this->request['id_token'], $public_key['key'], array('RS256'));
-        } catch(\Exception $e) {
-            var_dump($e);
+        } catch(ExpiredException $e) {
             // Error validating signature.
             throw new LTI_Exception("Invalid signature on id_token", 1);
         }
@@ -310,8 +321,12 @@ private function validate_jwt_signature() {
     }
 
     private function validate_deployment() {
+        if (!isset($this->jwt['body'][LTI_Constants::DEPLOYMENT_ID])) {
+            throw new LTI_Exception("No deployment ID was specified", 1);
+        }
+
         // Find deployment.
-        $deployment = $this->db->find_deployment($this->jwt['body']['iss'], $this->jwt['body']['https://purl.imsglobal.org/spec/lti/claim/deployment_id']);
+        $deployment = $this->db->find_deployment($this->jwt['body']['iss'], $this->jwt['body'][LTI_Constants::DEPLOYMENT_ID]);
 
         if (empty($deployment)) {
             // deployment not recognized.
@@ -322,7 +337,7 @@ private function validate_deployment() {
     }
 
     private function validate_message() {
-        if (empty($this->jwt['body']['https://purl.imsglobal.org/spec/lti/claim/message_type'])) {
+        if (empty($this->jwt['body'][LTI_Constants::MESSAGE_TYPE])) {
             // Unable to identify message type.
             throw new LTI_Exception("Invalid message type", 1);
         }
@@ -369,4 +384,4 @@ private function validate_message() {
 
     }
 }
-?>
\ No newline at end of file
+
diff --git a/src/lti/LTI_Names_Roles_Provisioning_Service.php b/src/lti/LTI_Names_Roles_Provisioning_Service.php
index df2242ea..e22b594d 100644
--- a/src/lti/LTI_Names_Roles_Provisioning_Service.php
+++ b/src/lti/LTI_Names_Roles_Provisioning_Service.php
@@ -1,44 +1,43 @@
-<?php
-namespace IMSGlobal\LTI;
-
-class LTI_Names_Roles_Provisioning_Service {
-
-    private $service_connector;
-    private $service_data;
-
-    public function __construct(LTI_Service_Connector $service_connector, $service_data) {
-        $this->service_connector = $service_connector;
-        $this->service_data = $service_data;
-    }
-
-    public function get_members() {
-
-        $members = [];
-
-        $next_page = $this->service_data['context_memberships_url'];
-
-        while ($next_page) {
-            $page = $this->service_connector->make_service_request(
-                ['https://purl.imsglobal.org/spec/lti-nrps/scope/contextmembership.readonly'],
-                'GET',
-                $next_page,
-                null,
-                null,
-                'application/vnd.ims.lti-nrps.v2.membershipcontainer+json'
-            );
-
-            $members = array_merge($members, $page['body']['members']);
-
-            $next_page = false;
-            foreach($page['headers'] as $header) {
-                if (preg_match(LTI_Service_Connector::NEXT_PAGE_REGEX, $header, $matches)) {
-                    $next_page = $matches[1];
-                    break;
-                }
-            }
-        }
-        return $members;
-
-    }
-}
-?>
+<?php
+namespace IMSGlobal\LTI;
+
+class LTI_Names_Roles_Provisioning_Service {
+
+    private $service_connector;
+    private $service_data;
+
+    public function __construct(LTI_Service_Connector $service_connector, $service_data) {
+        $this->service_connector = $service_connector;
+        $this->service_data = $service_data;
+    }
+
+    public function get_members() {
+
+        $members = [];
+
+        $next_page = $this->service_data['context_memberships_url'];
+
+        while ($next_page) {
+            $page = $this->service_connector->make_service_request(
+                [LTI_Constants::NRPS_CONTEXT_MEMBERSHIP_READ_ONLY],
+                'GET',
+                $next_page,
+                null,
+                null,
+                'application/vnd.ims.lti-nrps.v2.membershipcontainer+json'
+            );
+
+            $members = array_merge($members, $page['body']['members']);
+
+            $next_page = false;
+            foreach($page['headers'] as $header) {
+                if (preg_match(LTI_Service_Connector::NEXT_PAGE_REGEX, $header, $matches)) {
+                    $next_page = $matches[1];
+                    break;
+                }
+            }
+        }
+        return $members;
+
+    }
+}
diff --git a/src/lti/LTI_OIDC_Login.php b/src/lti/LTI_OIDC_Login.php
index 2c135c09..4c43aa66 100644
--- a/src/lti/LTI_OIDC_Login.php
+++ b/src/lti/LTI_OIDC_Login.php
@@ -3,6 +3,8 @@
 
 class LTI_OIDC_Login {
 
+    public const COOKIE_PREFIX = 'lti1p3_';
+
     private $db;
     private $cache;
     private $cookie;
@@ -17,12 +19,12 @@ class LTI_OIDC_Login {
     function __construct(Database $database, Cache $cache = null, Cookie $cookie = null) {
         $this->db = $database;
         if ($cache === null) {
-            $cache = new Cache();
+            $cache = new ImsCache();
         }
         $this->cache = $cache;
 
         if ($cookie === null) {
-            $cookie = new Cookie();
+            $cookie = new ImsCookie();
         }
         $this->cookie = $cookie;
     }
@@ -62,7 +64,7 @@ public function do_oidc_login_redirect($launch_url, array $request = null) {
         // Generate State.
         // Set cookie (short lived)
         $state = str_replace('.', '_', uniqid('state-', true));
-        $this->cookie->set_cookie("lti1p3_$state", $state, 60);
+        $this->cookie->set_cookie(static::COOKIE_PREFIX.$state, $state, 60);
 
         // Generate Nonce.
         $nonce = uniqid('nonce-', true);
@@ -117,4 +119,4 @@ protected function validate_oidc_login($request) {
         // Return Registration.
         return $registration;
     }
-}
\ No newline at end of file
+}
diff --git a/src/lti/LTI_Registration.php b/src/lti/LTI_Registration.php
index 7438253c..3a5bbac2 100644
--- a/src/lti/LTI_Registration.php
+++ b/src/lti/LTI_Registration.php
@@ -90,4 +90,3 @@ public function set_kid($kid) {
 
 }
 
-?>
\ No newline at end of file
diff --git a/src/lti/LTI_Service_Connector.php b/src/lti/LTI_Service_Connector.php
index cd2318e5..9863606a 100644
--- a/src/lti/LTI_Service_Connector.php
+++ b/src/lti/LTI_Service_Connector.php
@@ -90,4 +90,3 @@ public function make_service_request($scopes, $method, $url, $body = null, $cont
         ];
     }
 }
-?>
\ No newline at end of file
diff --git a/src/lti/Message_Validator.php b/src/lti/Message_Validator.php
index d12be20b..6ef79e46 100644
--- a/src/lti/Message_Validator.php
+++ b/src/lti/Message_Validator.php
@@ -5,4 +5,3 @@ interface Message_Validator {
     public function validate($jwt_body);
     public function can_validate($jwt_body);
 }
-?>
\ No newline at end of file
diff --git a/src/lti/OIDC_Exception.php b/src/lti/OIDC_Exception.php
index d492f4d2..9efcce64 100644
--- a/src/lti/OIDC_Exception.php
+++ b/src/lti/OIDC_Exception.php
@@ -4,4 +4,3 @@
 class OIDC_Exception extends \Exception {
 
 }
-?>
\ No newline at end of file
diff --git a/src/lti/Redirect.php b/src/lti/Redirect.php
index 647e8f44..20ca2e2b 100644
--- a/src/lti/Redirect.php
+++ b/src/lti/Redirect.php
@@ -19,7 +19,7 @@ public function do_redirect() {
 
     public function do_hybrid_redirect(Cookie $cookie = null) {
         if ($cookie == null) {
-            $cookie = new Cookie();
+            $cookie = new ImsCookie();
         }
         if (!empty($cookie->get_cookie(self::$CAN_302_COOKIE))) {
             return $this->do_redirect();
@@ -79,5 +79,3 @@ public function do_js_redirect() {
     }
 
 }
-
-?>
\ No newline at end of file
diff --git a/src/lti/lti.php b/src/lti/lti.php
index 67d9a04c..5a5c2181 100644
--- a/src/lti/lti.php
+++ b/src/lti/lti.php
@@ -5,4 +5,3 @@
 }
 define("TOOL_HOST", ($_SERVER['HTTP_X_FORWARDED_PROTO'] ?: $_SERVER['REQUEST_SCHEME']) . '://' . $_SERVER['HTTP_HOST']);
 Firebase\JWT\JWT::$leeway = 5;
-?>
\ No newline at end of file
diff --git a/src/lti/message_validators/deep_link_message_validator.php b/src/lti/message_validators/deep_link_message_validator.php
index eefb746a..2425b1ea 100644
--- a/src/lti/message_validators/deep_link_message_validator.php
+++ b/src/lti/message_validators/deep_link_message_validator.php
@@ -3,23 +3,23 @@
 
 class Deep_Link_Message_Validator implements Message_Validator {
     public function can_validate($jwt_body) {
-        return $jwt_body['https://purl.imsglobal.org/spec/lti/claim/message_type'] === 'LtiDeepLinkingRequest';
+        return $jwt_body[LTI_Constants::MESSAGE_TYPE] === 'LtiDeepLinkingRequest';
     }
 
     public function validate($jwt_body) {
         if (empty($jwt_body['sub'])) {
             throw new LTI_Exception('Must have a user (sub)');
         }
-        if ($jwt_body['https://purl.imsglobal.org/spec/lti/claim/version'] !== '1.3.0') {
+        if ($jwt_body[LTI_Constants::VERSION] !== LTI_Constants::V1_3) {
             throw new LTI_Exception('Incorrect version, expected 1.3.0');
         }
-        if (!isset($jwt_body['https://purl.imsglobal.org/spec/lti/claim/roles'])) {
+        if (!isset($jwt_body[LTI_Constants::ROLES])) {
             throw new LTI_Exception('Missing Roles Claim');
         }
-        if (empty($jwt_body['https://purl.imsglobal.org/spec/lti-dl/claim/deep_linking_settings'])) {
+        if (empty($jwt_body[LTI_Constants::DL_DEEP_LINK_SETTINGS])) {
             throw new LTI_Exception('Missing Deep Linking Settings');
         }
-        $deep_link_settings = $jwt_body['https://purl.imsglobal.org/spec/lti-dl/claim/deep_linking_settings'];
+        $deep_link_settings = $jwt_body[LTI_Constants::DL_DEEP_LINK_SETTINGS];
         if (empty($deep_link_settings['deep_link_return_url'])) {
             throw new LTI_Exception('Missing Deep Linking Return URL');
         }
@@ -33,4 +33,3 @@ public function validate($jwt_body) {
         return true;
     }
 }
-?>
\ No newline at end of file
diff --git a/src/lti/message_validators/resource_message_validator.php b/src/lti/message_validators/resource_message_validator.php
index 22521167..65559afc 100644
--- a/src/lti/message_validators/resource_message_validator.php
+++ b/src/lti/message_validators/resource_message_validator.php
@@ -3,24 +3,26 @@
 
 class Resource_Message_Validator implements Message_Validator {
     public function can_validate($jwt_body) {
-        return $jwt_body['https://purl.imsglobal.org/spec/lti/claim/message_type'] === 'LtiResourceLinkRequest';
+        return $jwt_body[LTI_Constants::MESSAGE_TYPE] === 'LtiResourceLinkRequest';
     }
 
     public function validate($jwt_body) {
         if (empty($jwt_body['sub'])) {
             throw new LTI_Exception('Must have a user (sub)');
         }
-        if ($jwt_body['https://purl.imsglobal.org/spec/lti/claim/version'] !== '1.3.0') {
+        if (!isset($jwt_body[LTI_Constants::VERSION])) {
+            throw new LTI_Exception('Missing LTI Version');
+        }
+        if ($jwt_body[LTI_Constants::VERSION] !== LTI_Constants::V1_3) {
             throw new LTI_Exception('Incorrect version, expected 1.3.0');
         }
-        if (!isset($jwt_body['https://purl.imsglobal.org/spec/lti/claim/roles'])) {
+        if (!isset($jwt_body[LTI_Constants::ROLES])) {
             throw new LTI_Exception('Missing Roles Claim');
         }
-        if (empty($jwt_body['https://purl.imsglobal.org/spec/lti/claim/resource_link']['id'])) {
+        if (empty($jwt_body[LTI_Constants::RESOURCE_LINK]['id'])) {
             throw new LTI_Exception('Missing Resource Link Id');
         }
 
         return true;
     }
 }
-?>
\ No newline at end of file