Restricting nginx website connection to VPN Users on the same server

My main aim is the following: Install a VPN server on a server, and a website on that server should be accessible only to users that are using the VPN on that same server.

First, the two server case works.

That is, I have two servers, A and B. The PPTP VPN server is installed in A, and the nginx is on B.

I have set up allow rules for my nginx site as follows and they work OK:

allow ip_of_a;
deny all;

However, when I try to connect a site on A (the vpn server has an nginx server too), my remote IP appears as my original IP, not the IP I get when I connect through VPN and I get a 403 Forbidden page on nginx. The error logs show a connection attempt from my original ip, not the VPN's IP.

I understand that the VPN still knows my original IP instead of the ip it gave to me, but there should be a workaround for this situation.

The VPN assigns local IP's of the form allow 10.80.80.*, so I put another allow of the form

allow 10.80.80.0/24;

That did not do the trick.

I also tried directly adding the local ip the VPN gives to me, but again it did not work:

allow 10.80.80.100;

Does this need to fixed from the pptp server somehow or can it be fixed from an nginx rule?

Edit: The routing tables on the client (OS X) before and afterconnecting to the vpn:

Before:

Internet:
Destination        Gateway            Flags        Refs      Use   Netif Expire
default            192.168.1.1        UGSc           18        0     en0
127                127.0.0.1          UCS             0        0     lo0
127.0.0.1          127.0.0.1          UH             17 12724964     lo0
169.254            link#4             UCS             0        0     en0
192.168.1          link#4             UCS             3        0     en0
192.168.1.1        0:25:9c:4a:c6:44   UHLWIir        19    28906     en0   1000
192.168.1.126      0:88:65:5c:6a:f4   UHLWIi          0       33     en0    440
192.168.1.129      127.0.0.1          UHS             1        0     lo0
192.168.1.255      ff:ff:ff:ff:ff:ff  UHLWbI          0       24     en0

After:

Internet:
Destination        Gateway            Flags        Refs      Use   Netif Expire
default            10.99.99.99        UGSc           16        0    ppp0
default            192.168.1.1        UGScI          11        0     en0
10                 ppp0               USc             1        0    ppp0
10.99.99.99        10.99.99.100       UHr            17        8    ppp0
SERVER_IP_HERE      192.168.1.1        UGHS            1      299     en0
127                127.0.0.1          UCS             0        0     lo0
127.0.0.1          127.0.0.1          UH             17 12724968     lo0
169.254            link#4             UCS             0        0     en0
192.168.1          link#4             UCS             3        0     en0
192.168.1.1        0:25:9c:4a:c6:44   UHLWIir        13    28987     en0    988
192.168.1.126      0:88:65:5c:6a:f4   UHLWIi          0       33     en0    428
192.168.1.129      127.0.0.1          UHS             0        0     lo0
192.168.1.255      ff:ff:ff:ff:ff:ff  UHLWbI          0       38     en0

VPN server don't redirect web trafic by default, as explained here, adding the line

push "redirect-gateway def1"

on your openvpn.conf will permit you to have the VPN server IP as your remote IP, and with that your web server should let you pass.