Implement automatic VPN login generation

coin/vpn/models.py

@@ -20,7 +20,8 @@ class VPNSubscription(CoinLdapSyncMixin, models.Model):
         related_name=backend_name,
         validators=[ValidateBackendType(backend_name)])
     activated = models.BooleanField(default=False)
-    login = models.CharField(max_length=50, unique=True)
+    login = models.CharField(max_length=50, unique=True, blank=True,
+                             help_text="leave empty for automatic generation")
     password = models.CharField(max_length=256, blank=True, null=True)
     ipv4_endpoint = InetAddressField(validators=[validation.validate_v4],
                                      blank=True, null=True)
@@ -110,6 +111,20 @@ class VPNSubscription(CoinLdapSyncMixin, models.Model):
                 raise ValidationError("Endpoint {} is not in an attributed range".format(self.ipv6_endpoint))
 
     def clean(self):
+        # Generate VPN login, of the form "user_vpnX"
+        if not self.login:
+            username = self.administrative_subscription.member.ldap_cn
+            vpns = VPNSubscription.objects.filter(administrative_subscription__member__ldap_cn=username)
+            # This is the list of existing VPN logins for this user.
+            logins = [vpn.login for vpn in vpns]
+            # 100 VPNs ought to be enough for anybody.
+            for login in ["{}-vpn{}".format(username, k) for k in range(1, 101)]:
+                if login not in logins:
+                    self.login = login
+                    break
+            # We may have failed.
+            if not self.login:
+                ValidationError("Unable to allocate a VPN login.")
         # Hash password if needed
         self.password = utils.ldap_hash(self.password)
         # If saving for the first time and IP endpoints are not specified,