diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 38080af1..627ad8b3 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -20,7 +20,7 @@ jobs:
             fail-fast: false
             matrix:
                 os: [ubuntu-latest]
-                php: ['7.0', '7.1', '7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3']
+                php: ['7.1', '7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3', '8.4']
 
         steps:
             - name: Checkout
diff --git a/README.md b/README.md
index 904b83ec..a4eb592d 100644
--- a/README.md
+++ b/README.md
@@ -7,7 +7,7 @@ the OpenID Connect protocol to set up authentication.
 A special thanks goes to Justin Richer and Amanda Anganes for their help and support of the protocol.
 
 # Requirements #
- 1. PHP 7.0 or greater
+ 1. PHP 7.1 or greater
  2. CURL extension
  3. JSON extension
 
diff --git a/composer.json b/composer.json
index 64825884..dc24d01b 100644
--- a/composer.json
+++ b/composer.json
@@ -3,7 +3,7 @@
     "description": "Bare-bones OpenID Connect client",
     "license": "Apache-2.0",
     "require": {
-        "php": ">=7.0",
+        "php": ">=7.1",
         "ext-json": "*",
         "ext-curl": "*",
         "phpseclib/phpseclib": "^3.0.7"
diff --git a/src/OpenIDConnectClient.php b/src/OpenIDConnectClient.php
index 07c00540..f7808402 100644
--- a/src/OpenIDConnectClient.php
+++ b/src/OpenIDConnectClient.php
@@ -259,7 +259,7 @@ class OpenIDConnectClient
      * @param string|null $client_secret optional
      * @param string|null $issuer
      */
-    public function __construct(string $provider_url = null, string $client_id = null, string $client_secret = null, string $issuer = null) {
+    public function __construct(?string $provider_url = null, ?string $client_id = null, ?string $client_secret = null, ?string $issuer = null) {
         $this->setProviderURL($provider_url);
         if ($issuer === null) {
             $this->setIssuer($provider_url);
@@ -1189,7 +1189,7 @@ protected function validateIssuer(string $iss): bool
      * @return bool
      * @throws OpenIDConnectClientException
      */
-    protected function verifyJWTClaims($claims, string $accessToken = null): bool
+    protected function verifyJWTClaims($claims, ?string $accessToken = null): bool
     {
         if(isset($claims->at_hash, $accessToken)) {
             if(isset($this->getIdTokenHeader()->alg) && $this->getIdTokenHeader()->alg !== 'none') {
@@ -1258,7 +1258,7 @@ protected function decodeJWT(string $jwt, int $section = 0) {
      *
      * @throws OpenIDConnectClientException
      */
-    public function requestUserInfo(string $attribute = null) {
+    public function requestUserInfo(?string $attribute = null) {
 
         $user_info_endpoint = $this->getProviderConfigValue('userinfo_endpoint');
         $schema = 'openid';
@@ -1335,7 +1335,7 @@ public function requestUserInfo(string $attribute = null) {
      * @return mixed
      *
      */
-    public function getVerifiedClaims(string $attribute = null) {
+    public function getVerifiedClaims(?string $attribute = null) {
 
         if($attribute === null) {
             return $this->verifiedClaims;
@@ -1355,7 +1355,7 @@ public function getVerifiedClaims(string $attribute = null) {
      * @return bool|string
      * @throws OpenIDConnectClientException
      */
-    protected function fetchURL(string $url, string $post_body = null, array $headers = []) {
+    protected function fetchURL(string $url, ?string $post_body = null, array $headers = []) {
 
         // OK cool - then let's create a new cURL resource handle
         $ch = curl_init();
@@ -1629,7 +1629,7 @@ public function register() {
      * @throws OpenIDConnectClientException
      * @throws Exception
      */
-    public function introspectToken(string $token, string $token_type_hint = '', string $clientId = null, string $clientSecret = null) {
+    public function introspectToken(string $token, string $token_type_hint = '', ?string $clientId = null, ?string $clientSecret = null) {
         $introspection_endpoint = $this->getProviderConfigValue('introspection_endpoint');
         $token_endpoint_auth_methods_supported = $this->getProviderConfigValue('token_endpoint_auth_methods_supported', ['client_secret_basic']);
 
@@ -1670,7 +1670,7 @@ public function introspectToken(string $token, string $token_type_hint = '', str
      * @return mixed
      * @throws OpenIDConnectClientException
      */
-    public function revokeToken(string $token, string $token_type_hint = '', string $clientId = null, string $clientSecret = null) {
+    public function revokeToken(string $token, string $token_type_hint = '', ?string $clientId = null, ?string $clientSecret = null) {
         $revocation_endpoint = $this->getProviderConfigValue('revocation_endpoint');
 
         $post_data = ['token' => $token];