feat(auth,ui): support github sign-in in the UI (#2545)

# What does this PR do?
Uses NextAuth to add github sign in support.

## Test Plan
Start server with auth configured as in
https://github.com/meta-llama/llama-stack/pull/2509


https://github.com/user-attachments/assets/61ff7442-f601-4b39-8686-5d0afb3b45ac

llama_stack/ui/lib/auth.ts

@@ -0,0 +1,38 @@
+import { NextAuthOptions } from "next-auth";
+import GithubProvider from "next-auth/providers/github";
+
+export const authOptions: NextAuthOptions = {
+  providers: [
+    GithubProvider({
+      clientId: process.env.GITHUB_CLIENT_ID!,
+      clientSecret: process.env.GITHUB_CLIENT_SECRET!,
+      authorization: {
+        params: {
+          scope: "read:user user:email",
+        },
+      },
+    }),
+  ],
+  debug: process.env.NODE_ENV === "development",
+  callbacks: {
+    async jwt({ token, account }) {
+      // Persist the OAuth access_token to the token right after signin
+      if (account) {
+        token.accessToken = account.access_token;
+      }
+      return token;
+    },
+    async session({ session, token }) {
+      // Send properties to the client, like an access_token from a provider.
+      session.accessToken = token.accessToken as string;
+      return session;
+    },
+  },
+  pages: {
+    signIn: "/auth/signin",
+    error: "/auth/signin", // Redirect errors to our custom page
+  },
+  session: {
+    strategy: "jwt",
+  },
+};

llama_stack/ui/lib/client.ts

@@ -1,6 +0,0 @@
-import LlamaStackClient from "llama-stack-client";
-
-export const client = new LlamaStackClient({
-  baseURL:
-    typeof window !== "undefined" ? `${window.location.origin}/api` : "/api",
-});

llama_stack/ui/lib/config-validator.ts

@@ -0,0 +1,56 @@
+/**
+ * Validates environment configuration for the application
+ * This is called during server initialization
+ */
+export function validateServerConfig() {
+  if (process.env.NODE_ENV === "development") {
+    console.log("🚀 Starting Llama Stack UI Server...");
+
+    // Check optional configurations
+    const optionalConfigs = {
+      NEXTAUTH_URL: process.env.NEXTAUTH_URL || "http://localhost:8322",
+      LLAMA_STACK_BACKEND_URL:
+        process.env.LLAMA_STACK_BACKEND_URL || "http://localhost:8321",
+      LLAMA_STACK_UI_PORT: process.env.LLAMA_STACK_UI_PORT || "8322",
+      GITHUB_CLIENT_ID: process.env.GITHUB_CLIENT_ID,
+      GITHUB_CLIENT_SECRET: process.env.GITHUB_CLIENT_SECRET,
+    };
+
+    console.log("\n📋 Configuration:");
+    console.log(`   - NextAuth URL: ${optionalConfigs.NEXTAUTH_URL}`);
+    console.log(`   - Backend URL: ${optionalConfigs.LLAMA_STACK_BACKEND_URL}`);
+    console.log(`   - UI Port: ${optionalConfigs.LLAMA_STACK_UI_PORT}`);
+
+    // Check GitHub OAuth configuration
+    if (
+      !optionalConfigs.GITHUB_CLIENT_ID ||
+      !optionalConfigs.GITHUB_CLIENT_SECRET
+    ) {
+      console.log(
+        "\n📝 GitHub OAuth not configured (authentication features disabled)",
+      );
+      console.log("   To enable GitHub OAuth:");
+      console.log("   1. Go to https://github.com/settings/applications/new");
+      console.log(
+        "   2. Set Application name: Llama Stack UI (or your preferred name)",
+      );
+      console.log("   3. Set Homepage URL: http://localhost:8322");
+      console.log(
+        "   4. Set Authorization callback URL: http://localhost:8322/api/auth/callback/github",
+      );
+      console.log(
+        "   5. Create the app and copy the Client ID and Client Secret",
+      );
+      console.log("   6. Add them to your .env.local file:");
+      console.log("      GITHUB_CLIENT_ID=your_client_id");
+      console.log("      GITHUB_CLIENT_SECRET=your_client_secret");
+    } else {
+      console.log("   - GitHub OAuth: ✅ Configured");
+    }
+
+    console.log("");
+  }
+}
+
+// Call this function when the module is imported
+validateServerConfig();