Add support for GitHub Enterprise (#24)

Author: retiman

package.json

@@ -1,6 +1,6 @@
 {
   "name": "github-app-token",
-  "version": "1.3.0",
+  "version": "1.4.0",
   "license": "MIT",
   "files": [
     "action.yml",

src/fetch-installation-token.ts

@@ -1,5 +1,6 @@
-import { context, getOctokit } from "@actions/github";
+import { getOctokit } from "@actions/github";
 import { createAppAuth } from "@octokit/auth-app";
+import { request } from "@octokit/request";
 
 export const fetchInstallationToken = async ({
   appId,
@@ -12,7 +13,15 @@ export const fetchInstallationToken = async ({
   privateKey: string;
   repo: string;
 }>): Promise<string> => {
-  const app = createAppAuth({ appId, privateKey });
+  const app = createAppAuth({
+    appId,
+    privateKey,
+    request: request.defaults({
+      // GITHUB_API_URL is part of GitHub Actions' built-in environment variables.
+      // See https://docs.github.com/en/actions/reference/environment-variables#default-environment-variables.
+      baseUrl: process.env["GITHUB_API_URL"]
+    })
+  });
   const authApp = await app({ type: "app" });
   const octokit = getOctokit(authApp.token);
   const {