clean up type mess in SSR functions

lib/session.ts

@@ -1,6 +1,15 @@
 import { withIronSession, Handler } from 'next-iron-session'
 import { getBaseURL } from '../helpers/url'
 
+export enum USER_ROLE {
+  ADMIN = 'admin',
+}
+
+export interface UserData {
+  username: string
+  role: USER_ROLE
+}
+
 const SESSION_SECRET =
   process.env.SESSION_SECRET || 'dev-env-default-secret-991823723'
 
@@ -16,13 +25,13 @@ export default function withSession(handler: Handler) {
   })
 }
 
-export function isAdminSession(req: any, res: any) {
-  const user = req?.session.get('user')
-  if (user && user.role === 'admin') {
+export function isAdminSession(req: any) {
+  const user = req?.session.get('user') as UserData
+  if (user && user.role === USER_ROLE.ADMIN) {
     return user
   }
 
-  return false
+  return null
 }
 
 export function redirectToLogin(req: any, res: any) {