simplegoproxy

simplegoproxy

Simplegoproxy is a http / API proxy that can, and is designed and intended to be used to modify the http request headers, response headers and / or response body on the fly, based on custom rules per request, and then return the modified response to the user.

Simply put, Simplegoproxy generates an "entrypoint url", which can be accessed (GET) to make an arbitrary http request to the "target url" (All aspects of the Request or Response can be set or modified), and returns the final result (modified Response) to the user.

Use cases:

• Remove CORS restrictions.
• Add "Authorization" or other headers to the request.
• Apply string replacements on the response body.

Run

Simplegoproxy is written in Go and published as a single executable file which requires no mandatory argument.

You can also run it using Docker:

docker run --name sgp -p 3000:3000 -d \
  ghcr.io/sagan/simplegoproxy

Command-line flag arguments:

  -key string
        The sign key. If set, all requests must be signed using HMAC(key, 'sha-256', payload=url), providing calculated MAC (hex string) in _sgp_sign
  -port int
        Http listening port (default 3000)
  -prefix string
        Prefix of settings in query parameters (default "_sgp_")
  -rootpath string
        Root path (with leading and trailing slash) (default "/")
  -sign
        Calculate the sign of target url and output result. The "key" flag need to be set. Args are url(s)

All arguments are optional, and can also be set by environment variable with the same name in uppercase, e.g.: "port" flag can also be set using "PORT" env.

Usage

Append the target url to the root path to generate the "entrypoint url". E.g.: (Assume Simplegoproxy is started with the default "/' root path):

curl -i "localhost:3000/https://ipcfg.co/json"

# The schema:// part of target url can be omitted, in which case "https://" is assumed
curl -i "localhost:3000/ipcfg.co/json"

The "entrypoint url" accepts GET requests only. By default it will just fetch the "target url" and return the original response, without any modification. Add specic query parameters to set the modification rules. E.g.:

curl -i "localhost:3000/https://ipcfg.co/json?_sgp_cors"

The _sgp_cors modification parameter indicates Simplegoproxy to modify the original response headers to set the CORS-allow-all headers:

Access-Control-Allow-Credentials: true
Access-Control-Allow-Methods: GET, OPTIONS
Access-Control-Allow-Origin: *

Modification parameters

All modification paramaters has the _sgp_ prefix by default, which can be changed via -prefix command-line argument.

• _sgp_cors : (Value ignored) Add the CORS-allow-all headers to original response.
• _sgp_nocsp : (Value ignored) Remove the Content Security Policy (CSP) headers from original response.
• _sgp_insecure : (Value ignored) Ignore any TLS cert error in http request.
• _sgp_proxy=socks5://1.2.3.4:1080 : Set the proxy for the http request.
• _sgp_timeout=5 : Set the timeout for the http request (seconds).
• _sgp_method=GET : Set the method for the http request. Default to GET.
• _sgp_header_<any>=<value> : Set the request header. E.g.: _sgp_header_Authorization=Token%20abcdef will set the "Authorization: Token abcdef" request header. If value is empty, will remove the target header from request.
• _sgp_resheader_<any>=<value> : Similar to _sgp_header_, but set or remove the response header.
• _sgp_sub_<string>=<replacement> : Similar to nginx http_sub module, modifiy the response by replacing one specified string by another. By default _sgp_sub_ rules only apply to the response with a "textual" MIME type, which could be any one of the following: "text/*", "application/json", "application/xml", "application/atom+xml", "application/x-sh".
• _sgp_forcesub : (Value ignored) Force apply _sgp_sub_ rules to the response of any MIME type.
• _sgp_cookie=<value> : Set request cookie. Equivalent to _sgp_header_cookie=<value>.
• _sgp_type=<value> : Set the request content type. Equivalent to _sgp_header_Content-Type=<value>. If _sgp_method is set to POST and _sgp_body is also set, the _sgp_type will have a default value application/x-www-form-urlencoded.
• _sgp_body=<value> : Set the request body (String only. Binary data is not supported).
• _sgp_fdheaders=<header1>,<header2>,... : Comma-separated forward headers list. For every header in the list, if the http request to the "entrypoint url" itself contains that header, Simplegoproxy will set the request header to the same value when making http request to the "target url". E.g.: _sgp_fdheaders=Referer,Origin. Note the following headers will ALWAYS be "forwarded", even if not set: "Range", "If-Range".
• _sgp_basicauth=user:password : Set the HTTP Basic Authentication for request. It can also be directly set in target url via "https://user:password@example.com" syntax.
• _sgp_impersonate=<value> : Impersonate itself as Browser when sending http request. See below.
• _sgp_sign : The sign of request canonical url. See below.

Modification paramaters are set in Query Variables. All _sgp_* parameters are stripped from the target url when Simplegoproxy fetch it. E.g.: the http://localhost:3000/https://ipcfg.co/json?abc=1&_sgp_cors entry will actually fetch the https://ipcfg.co/json?abc=1 target url.

All "escapable" characters in paramater name & value should be escaped in '%XX' format. (In general, the "escapable" means JavaScript's encodeURIComponent function return a escaped string for the char)

Other features

Modification parameters fronting

Instead of using Query Variables to set modification parameters, You can also put them in the "path", after the root path but before the target url. E.g.:

http://localhost:3000/_sgp_cors/https://ipcfg.co/json

Impersonate the Browser

Simplegoproxy can impersonate itself as Browser when sending http request to target url. It's similar to what curl-impersonate does. To enable this, set the _sgp_impersonate modification parameter to target browser name. E.g.:

http://localhost:3000/_sgp_impersonate=chrome120/https://ipcfg.co/json

Currently, only chrome120 (Chrome v120 on Windows 11 en-US) target is supported. Simplegoproxy will print the list of supported targets when starting.

Security tips

Set the rootpath

If your Simplegoproxy instance will be publicly accessible, make sure to set the "rootpath" flag to a "confidential" value other than the default "/". It acts like a password.

E.g.: If rootpath is set to "/abc/", then the entrypoint url should be like http://localhost:3000/abc/https://ipcfg.co/json.

Request signing

Additional, if "key" flag is set, all requests to Simplegoproxy must be signed via HMAC-SHA256 using the key. The message being signed is the "canonical url" of the request. The result MAC (message authentication code) should be provided in _sgp_sign parameter of the request.

The "canonical url" is the target url with all _sgp_* modification parameters (excluding _sgp_sign) in query values. All query values sorted by key.

To calculate the _sgp_sign value of a target url, run simplegoproxy with -sign flag. E.g.:

#simplegoproxy -sign -key abc "https://ipinfo.io/ip?_sgp_cors"
e9ccc14d94cd952d08bef094d9037c26b624a8bf18e6dc6c223d76224d4196ef  https://ipinfo.io/ip?_sgp_cors=

Then use the following entrypoint url :

http://localhost:3000/https://ipinfo.io/ip?_sgp_cors&_sgp_sign=e9ccc14d94cd952d08bef094d9037c26b624a8bf18e6dc6c223d76224d4196ef

# or
http://localhost:3000/_sgp_cors&_sgp_sign=e9ccc14d94cd952d08bef094d9037c26b624a8bf18e6dc6c223d76224d4196ef/https://ipinfo.io/ip

# or
http://localhost:3000/_sgp_sign=e9ccc14d94cd952d08bef094d9037c26b624a8bf18e6dc6c223d76224d4196ef/https://ipinfo.io/ip?_sgp_cors