KEYCLOAK-1033 Add PKCE support for JS Adapter

This adds support for the "S256" code_challenge_method to the JS Adapter.
Note that the method "plain" was deliberately left out as is not recommended
to be used in new applications.

Note that this PR includes two libraries:
- [base64-js]{@link https://github.com/beatgammit/base64-js}
- [js-sha256]{@link https://github.com/emn178/js-sha256}

`base64-js` is needed for cross-browser support for decoding the
Uint8ArrayBuffer returned by `crypto.getRandomValues` to a PKCE
compatible base64 string.

`js-sha256` library is required because the `crypto.subtle.digest`
support is not available for all browsers.

The PKCE codeVerifier is stored in the callbackStore of the JS Adapter.

Note: This PR is based on #5255 which got messed up during a rebase.

adapters/oidc/js/src/main/resources/keycloak.d.ts

@@ -34,7 +34,8 @@ declare namespace Keycloak {
 	type KeycloakResponseMode = 'query'|'fragment';
 	type KeycloakResponseType = 'code'|'id_token token'|'code id_token token';
 	type KeycloakFlow = 'standard'|'implicit'|'hybrid';
-	type KeycloakPromiseType = 'native'
+	type KeycloakPromiseType = 'native';
+	type KeycloakPkceMethod = 'S256';
 
 	interface KeycloakInitOptions {
 		/**
@@ -117,6 +118,13 @@ declare namespace Keycloak {
 		 * Keycloak specific promise objects.
 		 */
 		promiseType?: KeycloakPromiseType;
+
+		/**
+		 * Configures the Proof Key for Code Exchange (PKCE) method to use.
+		 * The currently allowed method is 'S256'.
+		 * If not configured, PKCE will not be used.
+		 */
+		pkceMethod?: KeycloakPkceMethod;
 	}
 
 	interface KeycloakLoginOptions {

testsuite/integration-arquillian/tests/base/src/main/java/org/keycloak/testsuite/util/javascript/JSObjectBuilder.java

@@ -69,6 +69,15 @@ public class JSObjectBuilder {
     }
 
 
+    public JSObjectBuilder pkceS256() {
+        return pkceMethod("S256");
+    }
+
+    private JSObjectBuilder pkceMethod(String method) {
+        arguments.put("pkceMethod", method);
+        return this;
+    }
+
     public String build() {
         StringBuilder argument = new StringBuilder("{");
         String comma = "";

testsuite/integration-arquillian/tests/base/src/test/java/org/keycloak/testsuite/javascript/JavascriptAdapterTest.java

@@ -142,6 +142,17 @@ public class JavascriptAdapterTest extends AbstractJavascriptTest {
                 .login("{kcLocale: 'en'}", assertLocaleIsSet("en"));
     }
 
+    @Test
+    public void testLoginWithPkceS256() {
+        JSObjectBuilder pkceS256 = defaultArguments().pkceS256();
+        testExecutor.init(pkceS256, this::assertInitNotAuth)
+                .login(this::assertOnLoginPage)
+                .loginForm(testUser, this::assertOnTestAppUrl)
+                .init(pkceS256, this::assertSuccessfullyLoggedIn)
+                .logout(this::assertOnTestAppUrl)
+                .init(pkceS256, this::assertInitNotAuth);
+    }
+
     @Test
     public void testRefreshToken() {
         testExecutor.init(defaultArguments(), this::assertInitNotAuth)