oauth2-proxyでGoogle sign in(Ubuntu 20.04)

サイトへのログインにGoogle認証を使いたくなったところに下の記事を見て[oauth2-proxy](https://github.com/oauth2-proxy/oauth2-proxy)を知り、早速導入しました。

https://qiita.com/tomoyk/items/2fdb2b014415026a0a39

前提として、NginxにLet's encryptを導入していました。

# nginx設定ファイル編集
手順は[oauth2-proxyのページ](https://github.com/oauth2-proxy/oauth2-proxy#installation)の通り。
nginxの設定だけ、少しはまりました。

最終的なnginxの設定はこちらです。
```configuration:oauth2-proxy.config
server {
  root /var/www/html;

  index index.html index.htm index.nginx-debian.html;

  server_name myserver.net;

  location /oauth2/ {
    proxy_pass       http://127.0.0.1:4180;
    proxy_set_header Host                    $host;
    proxy_set_header X-Real-IP               $remote_addr;
    proxy_set_header X-Scheme                $scheme;
    proxy_set_header X-Auth-Request-Redirect $request_uri;
    # or, if you are handling multiple domains:
    # proxy_set_header X-Auth-Request-Redirect $scheme://$host$request_uri;
  }
  location = /oauth2/auth {
    proxy_pass       http://127.0.0.1:4180;
    proxy_set_header Host             $host;
    proxy_set_header X-Real-IP        $remote_addr;
    proxy_set_header X-Scheme         $scheme;
    # nginx auth_request includes headers but not body
    proxy_set_header Content-Length   "";
    proxy_pass_request_body           off;
  }

  location / {
    auth_request /oauth2/auth;
    error_page 401 = /oauth2/sign_in;

    # pass information via X-User and X-Email headers to backend,
    # requires running with --set-xauthrequest flag
    auth_request_set $user   $upstream_http_x_auth_request_user;
    auth_request_set $email  $upstream_http_x_auth_request_email;
    proxy_set_header X-User  $user;
    proxy_set_header X-Email $email;

    # if you enabled --pass-access-token, this will pass the token to the backend
    auth_request_set $token  $upstream_http_x_auth_request_access_token;
    proxy_set_header X-Access-Token $token;

    # if you enabled --cookie-refresh, this is needed for it to work with auth_request
    auth_request_set $auth_cookie $upstream_http_set_cookie;
    add_header Set-Cookie $auth_cookie;

    # When using the --set-authorization-header flag, some provider's cookies can exceed the 4kb
    # limit and so the OAuth2 Proxy splits these into multiple parts.
    # Nginx normally only copies the first `Set-Cookie` header from the auth_request to the response,
    # so if your cookies are larger than 4kb, you will need to extract additional cookies manually.
    auth_request_set $auth_cookie_name_upstream_1 $upstream_cookie_auth_cookie_name_1;

    # Extract the Cookie attributes from the first Set-Cookie header and append them
    # to the second part ($upstream_cookie_* variables only contain the raw cookie content)
    if ($auth_cookie ~* "(; .*)") {
        set $auth_cookie_name_0 $auth_cookie;
        set $auth_cookie_name_1 "auth_cookie_name_1=$auth_cookie_name_upstream_1$1";
    }

    # Send both Set-Cookie headers now if there was a second part
    if ($auth_cookie_name_upstream_1) {
        add_header Set-Cookie $auth_cookie_name_0;
        add_header Set-Cookie $auth_cookie_name_1;
    }

    #proxy_pass http://127.0.0.1/;
    # or "root /path/to/site;" or "fastcgi_pass ..." etc
  }

  listen [::]:443 ssl ipv6only=on; # managed by Certbot
  listen 443 ssl; # managed by Certbot
  ssl_certificate /etc/letsencrypt/live/myserver.net/fullchain.pem; # managed by Certbot
  ssl_certificate_key /etc/letsencrypt/live/myserver.net/privkey.pem; # managed by Certbot
  include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
  ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot
}

server {
  if ($host = myserver.net) {
    return 301 https://$host$request_uri;
  } # managed by Certbot

  listen 80 default_server;
  listen [::]:80 default_server;

  server_name myserver.net;
    return 404; # managed by Certbot
}
```