simplegoproxy

README

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_norf : (Value ignored) Do not follow redirects.
• _sgp_nocache : (Value ignored) Add the no-cache headers to original response.
• _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. A special * value can be used to forward ALL request headers. The following headers will ALWAYS be forwarded, even if not specified, unless the same _sgp_header_* parameter is set: Authorization, Range, If-*; A special "\n" (%0A) value supresses this behavior and makes sure no headers would be forwarded.
• _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 "Impersonate the Browser" section.
• _sgp_sign=<value> : The sign of request canonical url. See below "Request signing" section.
• _sgp_scope=<value> : The scope of sign. Can be used multiple times. See below "Scope signing" section.
• _sgp_referer=<value> : Set the allowed referer of request to the entrypoint url. Can be used multiple times. See below "Referer restrictions" section.

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

Simplegoproxy will print the list of supported targets when starting. Currently supported impersonates:

• chrome120 : Chrome 120 on Windows 11 x64 en-US
• firefox121 : Firefox 121 on Windows 11 x64 en-US

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

Secret substitutions

If request signing is enabled, all __SECRET_**__ style substrings in modification parameter value or normal query variable will be replaced with the value of the corresponding SECRET_** environment variable, if it exists, when sending request to the target url.

The substitutions occur after the request signing verification.

Scope signing

If any none-empty _sgp_scope parameter is provided, the sign is calculated against the whole scope, which is a Chrome extension style match pattern, instead of against the single target url.

E.g.:

localhost:3000/_sgp_scope=https%3A%2F%2F%2A%2F%2A/ipinfo.io/ip

Here, the _sgp_scope is https://*/* , which matches all https URLs. The payload ("canonical target url") of scope signing is a ? character plus all _sgp_ parameters sorted by key. To calculate it:

simplegoproxy -sign -key abc "?_sgp_scope=https://*/*"
edb3aaafe81cc42ea94a862bb5b77b4876d39ab3748410716bc9d7041e64c715  ?_sgp_scope=https%3A%2F%2F%2A%2F%2A

Then use the following entrypoint url:

curl -i "localhost:3000/_sgp_sign=edb3aaafe81cc42ea94a862bb5b77b4876d39ab3748410716bc9d7041e64c715&_sgp_scope=https%3A%2F%2F%2A%2F%2A/ipinfo.io/ip"

The _sgp_scope parameter can be set multiple times. The sign can be used to access any target URL which matches with at least one provided scope.

Referer restrictions

If any _sgp_referer parameter is provided. Simplegoproxy will validate the Referer header of the request to the entrypoint url and only allow theses requests which referer match with at lease one provided _sgp_referer value.

The format of _sgp_referer should be a Chrome extension style match pattern (same as _sgp_scope). Additionaly, an empty value matches with the "Direct" request, in which case no Referer header is present.

Referer restrictions works even if request signing is not enabled.