OIDC: Added PKCE functionality

Related to #4734.
Uses core logic from League AbstractProvider.

app/Access/Oidc/OidcOAuthProvider.php

@@ -83,15 +83,9 @@ class OidcOAuthProvider extends AbstractProvider
 
     /**
      * Checks a provider response for errors.
-     *
-     * @param ResponseInterface $response
-     * @param array|string      $data     Parsed response data
-     *
      * @throws IdentityProviderException
-     *
-     * @return void
      */
-    protected function checkResponse(ResponseInterface $response, $data)
+    protected function checkResponse(ResponseInterface $response, $data): void
     {
         if ($response->getStatusCode() >= 400 || isset($data['error'])) {
             throw new IdentityProviderException(
@@ -105,13 +99,8 @@ class OidcOAuthProvider extends AbstractProvider
     /**
      * Generates a resource owner object from a successful resource owner
      * details request.
-     *
-     * @param array       $response
-     * @param AccessToken $token
-     *
-     * @return ResourceOwnerInterface
      */
-    protected function createResourceOwner(array $response, AccessToken $token)
+    protected function createResourceOwner(array $response, AccessToken $token): ResourceOwnerInterface
     {
         return new GenericResourceOwner($response, '');
     }
@@ -121,14 +110,18 @@ class OidcOAuthProvider extends AbstractProvider
      *
      * The grant that was used to fetch the response can be used to provide
      * additional context.
-     *
-     * @param array         $response
-     * @param AbstractGrant $grant
-     *
-     * @return OidcAccessToken
      */
-    protected function createAccessToken(array $response, AbstractGrant $grant)
+    protected function createAccessToken(array $response, AbstractGrant $grant): OidcAccessToken
     {
         return new OidcAccessToken($response);
     }
+
+    /**
+     * Get the method used for PKCE code verifier hashing, which is passed
+     * in the "code_challenge_method" parameter in the authorization request.
+     */
+    protected function getPkceMethod(): string
+    {
+        return static::PKCE_METHOD_S256;
+    }
 }

app/Access/Oidc/OidcService.php

@@ -33,6 +33,8 @@ class OidcService
 
     /**
      * Initiate an authorization flow.
+     * Provides back an authorize redirect URL, in addition to other
+     * details which may be required for the auth flow.
      *
      * @throws OidcException
      *
@@ -42,8 +44,12 @@ class OidcService
     {
         $settings = $this->getProviderSettings();
         $provider = $this->getProvider($settings);
+
+        $url = $provider->getAuthorizationUrl();
+        session()->put('oidc_pkce_code', $provider->getPkceCode() ?? '');
+
         return [
-            'url'   => $provider->getAuthorizationUrl(),
+            'url'   => $url,
             'state' => $provider->getState(),
         ];
     }
@@ -63,6 +69,10 @@ class OidcService
         $settings = $this->getProviderSettings();
         $provider = $this->getProvider($settings);
 
+        // Set PKCE code flashed at login
+        $pkceCode = session()->pull('oidc_pkce_code', '');
+        $provider->setPkceCode($pkceCode);
+
         // Try to exchange authorization code for access token
         $accessToken = $provider->getAccessToken('authorization_code', [
             'code' => $authorizationCode,