Add a method to guess organisation from a domain

We need this in the admin app while we still have pages that:
- talk about the data sharing and financial agreement
- but aren’t within a service (so can’t look at the service’s
  organisation)

This is a get, but it deliberately won’t work if you pass it an email
address, in order not to put personally identifying information in our
logs.

app/organisation/rest.py

@@ -1,10 +1,11 @@
-from flask import Blueprint, jsonify, request, current_app
+from flask import abort, Blueprint, jsonify, request, current_app
 from sqlalchemy.exc import IntegrityError
 
 from app.dao.organisation_dao import (
     dao_create_organisation,
     dao_get_organisations,
     dao_get_organisation_by_id,
+    dao_get_organisation_by_email_address,
     dao_get_organisation_services,
     dao_update_organisation,
     dao_add_service_to_organisation,
@@ -53,6 +54,24 @@ def get_organisation_by_id(organisation_id):
     return jsonify(organisation.serialize())
 
 
+@organisation_blueprint.route('/by-domain', methods=['GET'])
+def get_organisation_by_domain():
+
+    domain = request.args.get('domain')
+
+    if not domain or '@' in domain:
+        abort(400)
+
+    organisation = dao_get_organisation_by_email_address(
+        'example@{}'.format(request.args.get('domain'))
+    )
+
+    if not organisation:
+        abort(404)
+
+    return jsonify(organisation.serialize())
+
+
 @organisation_blueprint.route('', methods=['POST'])
 def create_organisation():
     data = request.get_json()