add signIn example

src/auth.ts

@@ -0,0 +1,77 @@
+import { AuthOptions, getServerSession } from "next-auth"
+import CredentialsProvider from "next-auth/providers/credentials";
+import { createAppClient, viemConnector } from "@farcaster/auth-client";
+
+declare module "next-auth" {
+  interface Session {
+    user: {
+      fid: number;
+    };
+  }
+}
+
+export const authOptions: AuthOptions = {
+    // Configure one or more authentication providers
+  providers: [
+    CredentialsProvider({
+      name: "Sign in with Farcaster",
+      credentials: {
+        message: {
+          label: "Message",
+          type: "text",
+          placeholder: "0x0",
+        },
+        signature: {
+          label: "Signature",
+          type: "text",
+          placeholder: "0x0",
+        },
+        // In a production app with a server, these should be fetched from
+        // your Farcaster data indexer rather than have them accepted as part
+        // of credentials.
+        name: {
+          label: "Name",
+          type: "text",
+          placeholder: "0x0",
+        },
+        pfp: {
+          label: "Pfp",
+          type: "text",
+          placeholder: "0x0",
+        },
+      },
+      async authorize(credentials, req) {
+        const csrfToken = req?.body?.csrfToken;
+        const appClient = createAppClient({
+          ethereum: viemConnector(),
+        });
+
+        const verifyResponse = await appClient.verifySignInMessage({
+          message: credentials?.message as string,
+          signature: credentials?.signature as `0x${string}`,
+          domain: process.env.NEXTAUTH_URL ?? '',
+          nonce: csrfToken,
+        });
+        const { success, fid } = verifyResponse;
+
+        if (!success) {
+          return null;
+        }
+
+        return {
+          id: fid.toString(),
+        };
+      },
+    }),
+  ],
+  callbacks: {
+    session: async ({ session, token }) => {
+      if (session?.user) {
+        session.user.fid = parseInt(token.sub ?? '');
+      }
+      return session;
+    },
+  }
+}
+
+export const getSession = () => getServerSession(authOptions)