code: function signout (idToken, postLogoutRedirectUri) {
    if (!idToken) {
      return Promise.reject(new Error('ID Token required for signout'))
    }
    var params = {}
    params.id_token_hint = idToken
    if (postLogoutRedirectUri) {
      params.post_logout_redirect_uri = postLogoutRedirectUri
    }
    var options = {
      endpoint: 'signout'
    }
    var uri = this.authorizationUri(options)
    var self = this
    var requestOptions = {
      url: uri,
      method: 'POST',
      json: params,
      agentOptions: self.agentOptions
    }
    if (self.proxy) {
      requestOptions.proxy = self.proxy
    }
  
    return Promise.resolve()
      .then(function () {
        return request(requestOptions)
      })
  }
docs: Sends a POST request to the provider's `/signout` endpoint, to end a user's
  session.
  @method signout
  @param idToken {String} ID Token of the user to sign out. Required.
  Used as `id_token_hint` by the OIDC provider
  @param [postLogoutRedirectUri] {String} Must be one of the post-logout uris
  pre-registered by the client.
  @return {Promise<Request>}