fix(auth0.checkSession): added an Auth0 check to see whether an Auth0 session already exists for the incoming user and redirects the user based on whether they have a valid session or not in Auth0 (#17753)

ui/src/Signin.tsx

@@ -2,6 +2,7 @@
 import React, {ReactElement, PureComponent} from 'react'
 import {withRouter, WithRouterProps} from 'react-router'
 import {connect} from 'react-redux'
+import auth0js from 'auth0-js'
 
 import {client} from 'src/utils/api'
 
@@ -83,10 +84,40 @@ export class Signin extends PureComponent<Props, State> {
       } = this.props
 
       clearInterval(this.intervalID)
+
       const config = await getAuth0Config()
       if (CLOUD && config.socialSignUpOn) {
-        this.props.router.replace('/login')
-        return
+        // The redirectUri must be the same as the url for the origin of the request
+        // otherwise there's a mismatch and Auth0 cannot validate the response
+        const redirectUri = window.location.href
+        // The responseType is arbitrary as it needs to be a non-empty, non "code" value:
+        // https://auth0.github.io/auth0.js/web-auth_index.js.html#line564
+        const responseType = 'token'
+
+        const auth0 = new auth0js.WebAuth({
+          domain: config.domain,
+          clientID: config.clientID,
+          redirectUri,
+          responseType,
+        })
+        // This is the result of JS & Auth0 weirdness
+        return new Promise((resolve, reject) => {
+          // The TLDR is that checkSession is not awaiting the callback to complete
+          // So checkSession can return a successful response and continue with the operation
+          // without the callback being completely finished
+          return auth0.checkSession({}, (error, webResponse) => {
+            if (error) {
+              reject(error)
+            }
+            resolve(webResponse)
+          })
+        })
+          .then(() => {
+            window.location.pathname = CLOUD_SIGNIN_PATHNAME
+          })
+          .catch(() => {
+            this.props.router.replace('/login')
+          })
       }
 
       // TODO: add returnTo to CLOUD signin