[bug] do not allow users to register with an invalid email address

CHANGELOG.md

@@ -23,6 +23,7 @@
 - Fix a bug: in the admin calendar, the trainings' info panel shows "duration: null minutes"
 - Fix a bug: on the subscriptions page, not logged-in users do not see the action button
 - Fix a bug: unable to map a new setup to the db network
+- Fix a bug: do not allow users to register with an invalid email address
 - Fix a security issue: updated dns-packet to 1.3.4 to fix [CVE-2021-23386](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-23386)
 - `SUPERADMIN_EMAIL` renamed to `ADMINSYS_EMAIL`
 - `scripts/run-tests.sh` renamed to `scripts/tests.sh`

app/frontend/templates/shared/signupModal.html

@@ -74,6 +74,7 @@
               <span class="input-group-addon"><i class="fa fa-envelope"></i></span>
               <input type="email"
                      name="email"
+                     ng-pattern="/^[^@]+@[^\.]+\..{2,}$/"
                      ng-model="user.email"
                      class="form-control"
                      placeholder="{{ 'app.public.common.your_email_address' | translate }}"