tests for JWTTokenProvider, verifying the "Authentication" header

This test basically ensures that the requests made with a
JWTTokenProvider follow a valid Authentication pattern,
verifying that the header "conforms" to a valid JWT token
More information on JWT tokens can be found at:

- https://jwt.io/introduction/

src/test/java/org/kohsuke/github/extras/auth/JWTTokenProviderTest.java

@@ -0,0 +1,48 @@
+package org.kohsuke.github.extras.auth;
+
+import java.io.File;
+import java.io.IOException;
+import java.security.GeneralSecurityException;
+
+import org.junit.Test;
+import org.kohsuke.github.AbstractGitHubWireMockTest;
+import org.kohsuke.github.GitHub;
+
+public class JWTTokenProviderTest extends AbstractGitHubWireMockTest {
+
+    private static String TEST_APP_ID_2 = "83009";
+    private static String PRIVATE_KEY_FILE_APP_2 = "/ghapi-test-app-2.private-key.pem";
+
+    /**
+     * This test will request an application ensuring that the header for the "Authorization" matches a valid JWT token.
+     * A JWT token in the Authorization header will always start with "ey" which is always the start of the base64
+     * encoding of the JWT Header , so a valid header will look like this:
+     *
+     * <pre>
+     * Authorization: Bearer ey{rest of the header}.{payload}.{signature}
+     * </pre>
+     *
+     * Matched by the regular expression:
+     *
+     * <pre>
+     * ^Bearer (?<JWTHeader>ey\S*)\.(?<JWTPayload>\S*)\.(?<JWTSignature>\S*)$
+     * </pre>
+     *
+     * Which is present in the wiremock matcher. Note that we need to use a matcher because the JWT token is encoded
+     * with a private key and a random nonce, so it will never be the same (under normal conditions). For more
+     * information on the format of a JWT token, see: https://jwt.io/introduction/
+     */
+    @Test
+    public void testAuthorizationHeaderPattern() throws GeneralSecurityException, IOException {
+        JWTTokenProvider jwtTokenProvider = new JWTTokenProvider(TEST_APP_ID_2,
+                new File(this.getClass().getResource(PRIVATE_KEY_FILE_APP_2).getFile()));
+        GitHub gh = getGitHubBuilder().withEndpoint(mockGitHub.apiServer().baseUrl())
+                .withAuthorizationProvider(jwtTokenProvider)
+                .build();
+
+        // Request the application, the wiremock matcher will ensure that the header
+        // for the authorization is present and has a the format of a valid JWT token
+        gh.getApp();
+    }
+
+}

src/test/resources/org/kohsuke/github/extras/auth/JWTTokenProviderTest/wiremock/testAuthorizationHeaderPattern/__files/app-1.json

@@ -0,0 +1,34 @@
+{
+  "id": 83009,
+  "slug": "ghapi-test-app-2",
+  "node_id": "MDM6QXBwODMwMDk=",
+  "owner": {
+    "login": "hub4j-test-org",
+    "id": 7544739,
+    "node_id": "MDEyOk9yZ2FuaXphdGlvbjc1NDQ3Mzk=",
+    "avatar_url": "https://avatars3.githubusercontent.com/u/7544739?v=4",
+    "gravatar_id": "",
+    "url": "https://api.github.com/users/hub4j-test-org",
+    "html_url": "https://github.com/hub4j-test-org",
+    "followers_url": "https://api.github.com/users/hub4j-test-org/followers",
+    "following_url": "https://api.github.com/users/hub4j-test-org/following{/other_user}",
+    "gists_url": "https://api.github.com/users/hub4j-test-org/gists{/gist_id}",
+    "starred_url": "https://api.github.com/users/hub4j-test-org/starred{/owner}{/repo}",
+    "subscriptions_url": "https://api.github.com/users/hub4j-test-org/subscriptions",
+    "organizations_url": "https://api.github.com/users/hub4j-test-org/orgs",
+    "repos_url": "https://api.github.com/users/hub4j-test-org/repos",
+    "events_url": "https://api.github.com/users/hub4j-test-org/events{/privacy}",
+    "received_events_url": "https://api.github.com/users/hub4j-test-org/received_events",
+    "type": "Organization",
+    "site_admin": false
+  },
+  "name": "GHApi Test app 2",
+  "description": "",
+  "external_url": "https://localhost",
+  "html_url": "https://github.com/apps/ghapi-test-app-2",
+  "created_at": "2020-09-30T15:02:20Z",
+  "updated_at": "2020-09-30T15:02:20Z",
+  "permissions": {},
+  "events": [],
+  "installations_count": 1
+}

src/test/resources/org/kohsuke/github/extras/auth/JWTTokenProviderTest/wiremock/testAuthorizationHeaderPattern/mappings/app-1.json

@@ -0,0 +1,44 @@
+{
+  "id": "bb7cf5bb-45b3-fba2-afd8-939b2c24787a",
+  "name": "app",
+  "request": {
+    "url": "/app",
+    "method": "GET",
+    "headers": {
+      "Authorization": {
+        "matches": "^Bearer (?<JWTHeader>ey\\S*)\\.(?<JWTPayload>\\S*)\\.(?<JWTSignature>\\S*)$"
+      },
+      "Accept": {
+        "equalTo": "application/vnd.github.machine-man-preview+json"
+      }
+    }
+  },
+  "response": {
+    "status": 200,
+    "bodyFileName": "app-1.json",
+    "headers": {
+      "Date": "Thu, 05 Nov 2020 20:42:31 GMT",
+      "Content-Type": "application/json; charset=utf-8",
+      "Server": "GitHub.com",
+      "Status": "200 OK",
+      "Cache-Control": "public, max-age=60, s-maxage=60",
+      "Vary": [
+        "Accept",
+        "Accept-Encoding, Accept, X-Requested-With",
+        "Accept-Encoding"
+      ],
+      "ETag": "W/\"b3d319dbb4dba93fbda071208d874e5ab566d827e1ad1d7dc59f26d68694dc48\"",
+      "X-GitHub-Media-Type": "github.v3; param=machine-man-preview; format=json",
+      "Strict-Transport-Security": "max-age=31536000; includeSubdomains; preload",
+      "X-Frame-Options": "deny",
+      "X-Content-Type-Options": "nosniff",
+      "X-XSS-Protection": "1; mode=block",
+      "Referrer-Policy": "origin-when-cross-origin, strict-origin-when-cross-origin",
+      "Content-Security-Policy": "default-src 'none'",
+      "X-GitHub-Request-Id": "9294:AE05:BDAC761:DB35838:5FA463B6"
+    }
+  },
+  "uuid": "bb7cf5bb-45b3-fba2-afd8-939b2c24787a",
+  "persistent": true,
+  "insertionIndex": 1
+}