server/auth.js

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.remoteBaseUrl + '/'
    )
    const search = new URLSearchParams()
    search.set('response_type', 'code')
    search.set('client_id', this.giteaClientId)
    search.set(
      'redirect_uri',
      this.remoteBaseUrl + '/auth/callback'
    )
    search.state = 'state'
    url.search = search.toString()
    return Response.redirect(url.toString())
  }
}