♻️ Update posthog identification flow (#686)

packages/backend/trpc/routers/whoami.ts

@@ -1,7 +1,10 @@
 import { prisma } from "@rallly/database";
+import { TRPCError } from "@trpc/server";
+import z from "zod";
 
+import { decryptToken } from "../../session";
 import { publicProcedure, router } from "../trpc";
-import { UserSession } from "../types";
+import { LoginTokenPayload, UserSession } from "../types";
 
 export const whoami = router({
   get: publicProcedure.query(async ({ ctx }): Promise<UserSession> => {
@@ -24,4 +27,34 @@ export const whoami = router({
   destroy: publicProcedure.mutation(async ({ ctx }) => {
     ctx.session.destroy();
   }),
+  authenticate: publicProcedure
+    .input(z.object({ token: z.string() }))
+    .mutation(async ({ ctx, input }) => {
+      const payload = await decryptToken<LoginTokenPayload>(input.token);
+
+      if (!payload) {
+        // token is invalid or expired
+        throw new TRPCError({ code: "PARSE_ERROR", message: "Invalid token" });
+      }
+
+      const user = await prisma.user.findFirst({
+        select: {
+          id: true,
+          name: true,
+          email: true,
+        },
+        where: { id: payload.userId },
+      });
+
+      if (!user) {
+        // user does not exist
+        throw new TRPCError({ code: "NOT_FOUND", message: "User not found" });
+      }
+
+      ctx.session.user = { id: user.id, isGuest: false };
+
+      await ctx.session.save();
+
+      return user;
+    }),
 });