server/auth.js

import * as cookie from 'https://deno.land/std@0.188.0/http/cookie.ts'

export class Auth {
  constructor({
    baseUrl,
    remoteBaseUrl,
    giteaAppBaseUrl,
    giteaClientId,
    giteaClientSecret
  }) {
    this.baseUrl = baseUrl
    this.remoteBaseUrl = remoteBaseUrl
    this.giteaAppBaseUrl = giteaAppBaseUrl
    this.giteaClientId = giteaClientId
    this.giteaClientSecret = giteaClientSecret
  }

  async redirect(event) {
    const url = new URL(
      this.giteaAppBaseUrl + '/login/oauth/authorize'
    )
    const search = new URLSearchParams()
    search.set('response_type', 'code')
    search.set('client_id', this.giteaClientId)
    search.set(
      'redirect_uri',
      this.remoteBaseUrl + '/auth/callback'
    )
    const timestamp = new Date().valueOf()
    const randomInt = Math.floor(Math.random() * 10000)
    // TODO: sign
    const state = `${randomInt}-${timestamp}`
    search.set('state', state)
    url.search = search.toString()
    const headers = new Headers({
      Location: url.toString()
    })
    cookie.setCookie(headers, {
      name: 'oauth.gitea.state',
      value: state,
    })
    return new Response('', {
      headers,
      status: 302,
    })
  }
}