Nginx reverse proxy with query parameter modification

I have an application that is not SSL aware behind nginx, thus I need to do the following

http://example.com/f1/f2/page?next_page=http%3A//example.com/f3/new_page

has to change to

https://example.com/f1/f2/page?next_page=https%3A//example.com/f3/new_page

So there's two things to do, change the scheme, which I was able to, and change the url param, which I've been somewhat successfull at, but it doesn't work completely.

I found a page that did what I want to do, but it doesn't work for me: https://blog.imaginea.com/modifying-query-parameters-nginx-in-reverse-proxy-mode/

relevant part of my nginx config:

server {
    listen 443 ssl;
    server_name example.com;

    ssl on;
    ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
    ssl_certificate /path/to/bundle.crt;
    ssl_certificate_key /path/to/bundle.key;
    ssl_ciphers HIGH:!aNULL:!eNULL:!EXPORT:!CAMELLIA:!DES:!MD5:!PSK:!RC4;
    ssl_prefer_server_ciphers on;

    underscores_in_headers on;
    rewrite_log on;

    location / {

        if ($args ~* (.*)(next_page=http%3A)(.*)) {
            set $args $1next_page=https%3A$3;
            rewrite ^(.*)$ $1;
        }

        proxy_pass http://127.0.0.1:80;
        proxy_redirect http:// https://;

        proxy_set_header Host $host;
        proxy_set_header HTTPS "on";
        proxy_set_header X-Real-IP  $remote_addr;
        proxy_set_header X-Forwarded-Host $host:$server_port;
        proxy_set_header X-Forwarded-Server $host;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto https;
        proxy_set_header X-Forwarded-Port 443;
    }
}

nginx_error.log:

2017/09/20 13:48:13 [notice] 25115#0: *1 "(.*)(next_page=http%3A)(.*)" matches "next_page=http%3A//example.com/f3/new_page", client: X.X.X.X, server: example.com, request: "GET /f1/f2/page?next_page=http%3A//example.com/f3/new_page HTTP/1.1", host: "example.com"
2017/09/20 13:48:13 [notice] 25115#0: *1 "^(.*)$" matches "/f1/f2/page", client: X.X.X.X, server: example.com, request: "GET /f1/f2/page?next_page=http%3A//example.com/f3/new_page HTTP/1.1", host: "example.com"
2017/09/20 13:48:13 [notice] 25115#0: *1 rewritten data: "/f1/f2/page", args: "next_page=https3A//example.com/f3/new_page", client: X.X.X.X, server: example.com, request: "GET /f1/f2/page?next_page=http%3A//example.com/f3/new_page HTTP/1.1", host: "example.com"
2017/09/20 13:48:13 [notice] 25115#0: *1 "(.*)(next_page=http%3A)(.*)" does not match "next_page=https3A//example.com/f3/new_page", client: X.X.X.X, server: example.com, request: "GET /f1/f2/page?next_page=http%3A//example.com/f3/new_page HTTP/1.1", host: "example.com"
2017/09/20 13:48:13 [notice] 25115#0: *1 "(.*)(next_page=http%3A)(.*)" does not match "", client: X.X.X.X, server: example.com, request: "GET /f1/f2/cookie/++resource++baseimg/regio.ico HTTP/1.1", host: "example.com", referrer: "https://example.com/f1/f2/page?next_page=http%3A//example.com/f3/new_page"

So the scheme get's changed by the proxy_redirect (I need to do this since occassionally the application itself will redirect to some http-URI), proxy_pass forwards it to the correct server and the args get changed, but the request does not. What am I missing here?

URL as shown in browser:

https://example.com/f1/f1/page?next_page=http%3A//example.com/f3/new_page

btw. nginx version is 1.10.1 and I am not able to upgrade it at this point