chore: migrate legacy pages and utilities to nuxt

frontend_nuxt/pages/github-callback.vue

@@ -0,0 +1,26 @@
+<template>
+  <CallbackPage />
+</template>
+
+<script>
+import CallbackPage from '../components/CallbackPage.vue'
+import { githubExchange } from '../utils/github'
+
+export default {
+  name: 'GithubCallbackPageView',
+  components: { CallbackPage },
+  async mounted() {
+    const url = new URL(window.location.href)
+    const code = url.searchParams.get('code')
+    const state = url.searchParams.get('state')
+    const result = await githubExchange(code, state, '')
+
+    if (result.needReason) {
+      this.$router.push('/signup-reason?token=' + result.token)
+    } else {
+      this.$router.push('/')
+    }
+  }
+}
+</script>
+