Add Firebase-powered GitHub login (#215)

This adds GitHub login via Firebase, as a foundation for adding a gallery (#26).  Currently it just adds a login/logout button to the Debug page.

At an architectural level, this adds an `AuthContext` React context, whose interface is generic enough that it's not coupled to Firebase or GitHub.  In fact, the default context is a "null context" whose operations are all no-ops.

lib/auth.tsx

@@ -0,0 +1,103 @@
+import { FirebaseApp, FirebaseOptions, initializeApp } from "firebase/app";
+import {
+  getAuth,
+  signInWithPopup,
+  GithubAuthProvider,
+  onAuthStateChanged,
+  signOut,
+  Auth,
+  User,
+} from "firebase/auth";
+import React, { useCallback, useEffect, useState } from "react";
+
+const DEFAULT_APP_CONFIG: FirebaseOptions = {
+  apiKey: "AIzaSyAV1kkVvSKEicEa8rLke9o_BxYBu1rb8kw",
+  authDomain: "mystic-addaf.firebaseapp.com",
+  projectId: "mystic-addaf",
+  storageBucket: "mystic-addaf.appspot.com",
+  messagingSenderId: "26787182745",
+  appId: "1:26787182745:web:e4fbd9439b9279fe966008",
+  measurementId: "G-JHKRSK1PR6",
+};
+
+/**
+ * Generic interface for authentication.
+ */
+export interface AuthContext {
+  /**
+   * The currently logged-in user. This will be
+   * null if the user isn't logged in, otherwise it will
+   * be their name.
+   */
+  loggedInUser: string | null;
+
+  /**
+   * The name of the authentication provider, e.g. "GitHub",
+   * or null if auth is disabled.
+   */
+  providerName: string | null;
+
+  /**
+   * If authentication failed for some reason, this will
+   * be a string describing the error.
+   */
+  error?: string;
+
+  /** Begin the login UI flow. */
+  login(): void;
+
+  /** Log out the user. */
+  logout(): void;
+}
+
+type FirebaseGithubAuthState = {
+  app: FirebaseApp;
+  auth: Auth;
+  provider: GithubAuthProvider;
+};
+
+/**
+ * A Firebase GitHub authentication provider.
+ *
+ * Note this component is assumed to never be unmounted, nor
+ * for its props to change.
+ */
+export const FirebaseGithubAuthProvider: React.FC<{
+  config?: FirebaseOptions;
+}> = ({ config, children }) => {
+  const [state, setState] = useState<FirebaseGithubAuthState | null>(null);
+  const [user, setUser] = useState<User | null>(null);
+  const [error, setError] = useState<string | undefined>(undefined);
+
+  const handleError = (e: Error) => setError(e.message);
+
+  useEffect(() => {
+    const app = initializeApp(config || DEFAULT_APP_CONFIG);
+    const auth = getAuth(app);
+    const provider = new GithubAuthProvider();
+
+    setState({ app, auth, provider });
+    onAuthStateChanged(auth, setUser);
+  }, [config]);
+
+  const context: AuthContext = {
+    loggedInUser: user && user.displayName,
+    providerName: "GitHub",
+    error,
+    login: useCallback(() => {
+      state && signInWithPopup(state.auth, state.provider).catch(handleError);
+    }, [state]),
+    logout: useCallback(() => {
+      state && signOut(state.auth).catch(handleError);
+    }, [state]),
+  };
+
+  return <AuthContext.Provider value={context} children={children} />;
+};
+
+export const AuthContext = React.createContext<AuthContext>({
+  loggedInUser: null,
+  providerName: null,
+  login() {},
+  logout() {},
+});

lib/browser-main.tsx

@@ -1,5 +1,6 @@
 import React, { useCallback, useEffect, useState } from "react";
 import ReactDOM from "react-dom";
+import { FirebaseGithubAuthProvider } from "./auth";
 import { PageContext, PAGE_QUERY_ARG } from "./page";
 import { pageNames, Pages, toPageName, DEFAULT_PAGE } from "./pages";
 
@@ -56,9 +57,11 @@ const App: React.FC<{}> = (props) => {
   };
 
   return (
-    <PageContext.Provider value={ctx}>
-      <PageComponent />
-    </PageContext.Provider>
+    <FirebaseGithubAuthProvider>
+      <PageContext.Provider value={ctx}>
+        <PageComponent />
+      </PageContext.Provider>
+    </FirebaseGithubAuthProvider>
   );
 };
 

lib/pages/debug-page.tsx

@@ -1,4 +1,5 @@
 import React, { useContext, useState } from "react";
+import { AuthContext } from "../auth";
 import { AutoSizingSvg } from "../auto-sizing-svg";
 import { CreatureContext, CreatureContextType } from "../creature-symbol";
 import { createCreatureSymbolFactory } from "../creature-symbol-factory";
@@ -93,6 +94,24 @@ const RandomColorSampling: React.FC<{}> = () => {
   );
 };
 
+const AuthWidget: React.FC<{}> = () => {
+  const ctx = useContext(AuthContext);
+
+  if (!ctx.providerName) {
+    return null;
+  }
+
+  if (ctx.error) {
+    return <p style={{ color: "red" }}>{ctx.error}</p>;
+  }
+
+  if (ctx.loggedInUser) {
+    return <button onClick={ctx.logout}>Logout {ctx.loggedInUser}</button>;
+  }
+
+  return <button onClick={ctx.login}>Login with {ctx.providerName}</button>;
+};
+
 export const DebugPage: React.FC<{}> = () => {
   const [symbolCtx, setSymbolCtx] = useState(createSvgSymbolContext());
   const defaultCtx = useContext(CreatureContext);
@@ -108,6 +127,7 @@ export const DebugPage: React.FC<{}> = () => {
         <SymbolContextWidget ctx={symbolCtx} onChange={setSymbolCtx} />
         <h2>Random color sampling</h2>
         <RandomColorSampling />
+        <AuthWidget />
       </div>
       <div className="canvas">
         <CreatureContext.Provider value={ctx}>

package.json

@@ -49,6 +49,7 @@
     "classnames": "^2.3.1",
     "colorspaces": "^0.1.5",
     "esbuild": "^0.12.5",
+    "firebase": "^9.0.0-beta.7",
     "gh-pages": "^3.1.0",
     "hsluv": "^0.1.0",
     "jest": "^26.6.3",