Refactor auth flow

Reimplement some node-oauth2-server methods to remove hacky code needed by our external
login workflow

server/lib/auth/tokens-cache.ts

@@ -0,0 +1,52 @@
+import * as LRUCache from 'lru-cache'
+import { MOAuthTokenUser } from '@server/types/models'
+import { LRU_CACHE } from '../../initializers/constants'
+
+export class TokensCache {
+
+  private static instance: TokensCache
+
+  private readonly accessTokenCache = new LRUCache<string, MOAuthTokenUser>({ max: LRU_CACHE.USER_TOKENS.MAX_SIZE })
+  private readonly userHavingToken = new LRUCache<number, string>({ max: LRU_CACHE.USER_TOKENS.MAX_SIZE })
+
+  private constructor () { }
+
+  static get Instance () {
+    return this.instance || (this.instance = new this())
+  }
+
+  hasToken (token: string) {
+    return this.accessTokenCache.has(token)
+  }
+
+  getByToken (token: string) {
+    return this.accessTokenCache.get(token)
+  }
+
+  setToken (token: MOAuthTokenUser) {
+    this.accessTokenCache.set(token.accessToken, token)
+    this.userHavingToken.set(token.userId, token.accessToken)
+  }
+
+  deleteUserToken (userId: number) {
+    this.clearCacheByUserId(userId)
+  }
+
+  clearCacheByUserId (userId: number) {
+    const token = this.userHavingToken.get(userId)
+
+    if (token !== undefined) {
+      this.accessTokenCache.del(token)
+      this.userHavingToken.del(userId)
+    }
+  }
+
+  clearCacheByToken (token: string) {
+    const tokenModel = this.accessTokenCache.get(token)
+
+    if (tokenModel !== undefined) {
+      this.userHavingToken.del(tokenModel.userId)
+      this.accessTokenCache.del(token)
+    }
+  }
+}