diff --git a/extensions/amp-access-laterpay/0.1/laterpay-impl.js b/extensions/amp-access-laterpay/0.1/laterpay-impl.js
index e11ea71d5e189..4f7905499a941 100644
--- a/extensions/amp-access-laterpay/0.1/laterpay-impl.js
+++ b/extensions/amp-access-laterpay/0.1/laterpay-impl.js
@@ -219,12 +219,13 @@ export class LaterpayVendor {
     const urlPromise = this.accessService_.buildUrl(
       url, /* useAuthData */ false);
     return urlPromise.then(url => {
-      dev().fine(TAG, 'Authorization URL: ', url);
+      return this.accessService_.buildLoginUrl(url);
+    }).then(url => {
+      dev().info(TAG, 'Authorization URL: ', url);
       return this.timer_.timeoutPromise(
           AUTHORIZATION_TIMEOUT,
           this.xhr_.fetchJson(url, {
             credentials: 'include',
-            requireAmpResponseSourceOrigin: true,
           }));
     });
   }
diff --git a/extensions/amp-access/0.1/amp-access.js b/extensions/amp-access/0.1/amp-access.js
index 0fac41e4cc119..a5172c99c594a 100644
--- a/extensions/amp-access/0.1/amp-access.js
+++ b/extensions/amp-access/0.1/amp-access.js
@@ -34,7 +34,7 @@ import {isExperimentOn} from '../../../src/experiments';
 import {isObject} from '../../../src/types';
 import {listenOnce} from '../../../src/event-helper';
 import {dev, user} from '../../../src/log';
-import {openLoginDialog} from './login-dialog';
+import {getLoginUrl, openLoginDialog} from './login-dialog';
 import {parseQueryString} from '../../../src/url';
 import {performanceForOrNull} from '../../../src/services';
 import {resourcesForDoc} from '../../../src/services';
@@ -157,6 +157,8 @@ export class AccessService {
     /** @private @const {function(string):Promise<string>} */
     this.openLoginDialog_ = openLoginDialog.bind(null, ampdoc);
 
+    this.getLoginUrl_ = getLoginUrl.bind(null, ampdoc);
+
     /** @private {?Promise<string>} */
     this.readerIdPromise_ = null;
 
@@ -919,8 +921,16 @@ export class AccessService {
     }
     return Promise.all(promises);
   }
-}
 
+  /**
+   * @param {string} url
+   * @return {string}
+   */
+  buildLoginUrl(url) {
+    return this.getLoginUrl_(url);
+  }
+
+}
 
 /**
  * @typedef {{
diff --git a/extensions/amp-access/0.1/login-dialog.js b/extensions/amp-access/0.1/login-dialog.js
index 30c5079997312..f267dba14ffa8 100644
--- a/extensions/amp-access/0.1/login-dialog.js
+++ b/extensions/amp-access/0.1/login-dialog.js
@@ -46,6 +46,15 @@ export function openLoginDialog(ampdoc, urlOrPromise) {
   return new WebLoginDialog(ampdoc.win, viewer, urlOrPromise).open();
 }
 
+export function getLoginUrl(ampdoc, urlOrPromise) {
+  const viewer = viewerForDoc(ampdoc);
+  const overrideDialog = parseInt(viewer.getParam('dialog'), 10);
+  if (overrideDialog) {
+    return new ViewerLoginDialog(viewer, urlOrPromise).getLoginUrl();
+  }
+  return new WebLoginDialog(ampdoc.win, viewer, urlOrPromise).getLoginUrl();
+}
+
 
 /**
  * The implementation of the Login Dialog delegated via Viewer.
@@ -63,13 +72,7 @@ class ViewerLoginDialog {
     this.urlOrPromise = urlOrPromise;
   }
 
-  /**
-   * Opens the dialog. Returns the promise that will yield with the dialog's
-   * result or will be rejected if dialog fails. The dialog's result is
-   * typically a hash string from the return URL.
-   * @return {!Promise<string>}
-   */
-  open() {
+  getLoginUrl() {
     let urlPromise;
     if (typeof this.urlOrPromise == 'string') {
       urlPromise = Promise.resolve(this.urlOrPromise);
@@ -77,13 +80,26 @@ class ViewerLoginDialog {
       urlPromise = this.urlOrPromise;
     }
     return urlPromise.then(url => {
-      const loginUrl = buildLoginUrl(url, 'RETURN_URL');
+      return buildLoginUrl(url, 'RETURN_URL');
+    });
+  }
+
+
+  /**
+   * Opens the dialog. Returns the promise that will yield with the dialog's
+   * result or will be rejected if dialog fails. The dialog's result is
+   * typically a hash string from the return URL.
+   * @return {!Promise<string>}
+   */
+  open() {
+    return this.getLoginUrl().then(loginUrl => {
       dev().fine(TAG, 'Open viewer dialog: ', loginUrl);
       return this.viewer.sendMessageAwaitResponse('openDialog', {
         'url': loginUrl,
       });
     });
   }
+
 }
 
 
@@ -172,6 +188,11 @@ export class WebLoginDialog {
     }
   }
 
+  getLoginUrl() {
+    const returnUrl = this.getReturnUrl_();
+    return buildLoginUrl(this.urlOrPromise, returnUrl);
+  }
+
   /** @private */
   openInternal_() {
     const screen = this.win.screen;
@@ -297,7 +318,6 @@ export class WebLoginDialog {
  * @param {string} url
  * @param {string} returnUrl
  * @return {string}
- * @private
  */
 function buildLoginUrl(url, returnUrl) {
   // RETURN_URL has to arrive here unreplaced by UrlReplacements for two