Added a new 400.html error page, this error page will only be used when we get an HTTPError from the api.

This was done to solve the problem of invitations expiring and the user getting a 500 error message, which says to try again.

app/__init__.py

@@ -5,6 +5,7 @@ from datetime import datetime, timedelta, timezone
 from time import monotonic
 
 import dateutil
+import itertools
 import pytz
 import ago
 from flask import (
@@ -37,7 +38,7 @@ from werkzeug.local import LocalProxy
 import app.proxy_fix
 from app.asset_fingerprinter import AssetFingerprinter
 from app.its_dangerous_session import ItsdangerousSessionInterface
-from app.notify_client.service_api_client import ServiceAPIClient
+from app.notify_client.service_api_client import ServiceAPIClient, ServicesBrowsableItem
 from app.notify_client.api_key_api_client import ApiKeyApiClient
 from app.notify_client.invite_api_client import InviteApiClient
 from app.notify_client.job_api_client import JobApiClient
@@ -405,7 +406,11 @@ def register_errorhandlers(application):
             error.message
         ))
         error_code = error.status_code
-        if error_code not in [401, 404, 403, 410, 500]:
+        if error_code == 400:
+            msg = list(itertools.chain(*[error.message[x] for x in error.message.keys()]))
+            resp = make_response(render_template("error/400.html", message=msg))
+            return useful_headers_after_request(resp)
+        elif error_code not in [401, 404, 403, 410, 500]:
             error_code = 500
         return _error_response(error_code)
 

app/templates/error/400.html

@@ -0,0 +1,11 @@
+{% extends "withoutnav_template.html" %}
+{% block page_title %}Bad Request{% endblock %}
+{% block maincolumn_content %}
+<div class="grid-row">
+    <div class="column-two-thirds">
+      <h1 class="heading-medium">
+            {{ message|join(",")}}
+        </h1>
+    </div>
+</div>
+{% endblock %}