Google OAuth2 uri_mismatch when behind an nginx reverse proxy

I'm trying a new server configuration using an nginx reverse proxy and ssl, but it seems to break my google OAuth2. I'm using node v6.2.2, pm2 to manage nodejs, and using nginx for ssl and a reverse proxy.

My Nginx server blocks look like:

server {
    listen 80;
    server_name _;
    return 301 https://$host$request_uri;
}

and

server {
    listen 443;
    ssl on;
    include snippets/ssl-example.com.conf;
    include snippets/ssl-params.conf;
    server_name example.com;
    location / {
            proxy_pass http://localhost:3001;
            proxy_http_version 1.1;
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection 'upgrade';
            proxy_set_header Host $host;
            proxy_cache_bypass $http_upgrade;
    }
}

When running the nodejs server on my laptop I'm able to login using passportjs' google strategy with no issues, but as soon as I run the same code behind the reverse proxy I get a redirect_uri_mismatch. I've tried hardcoding the callbackURL to http://example.com/auth/oauthCallback and https://example.com/auth/oauthCallback and have added all variations of those to the OAuth Client IDs. I've tried making small changes to my server blocks and couldn't make much headway, so here I am.

Any ideas for a next step?