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lua-resty-casbin

lua-resty-casbin is an authorization plugin/middleware for OpenResty, based on lua-casbin.

Installing OpenResty

You can follow this guide to install OpenResty on Ubuntu 20.04 if you have not yet installed it.

Installation

If you do not have LuaRocks installed for OpenResty then install it by:

sudo apt install make wget unzip zip

wget https://luarocks.org/releases/luarocks-3.3.1.tar.gz
tar zxpf luarocks-3.3.1.tar.gz
cd luarocks-3.3.1

./configure --prefix=/usr/local/openresty/luajit \
--with-lua=/usr/local/openresty/luajit/ \
--lua-suffix=jit-2.1.0-beta3 \
--with-lua-include=/usr/local/openresty/luajit/include/luajit-2.1

sudo make
sudo make install

NOTE:

• This is assuming OpenResty (not the executable) is installed at /usr/local/, if it isn't so - replace /usr/local/ with file path you have installed it in.
• Also assumed is that LuaJIT version is 2.1.0-beta3, you can check which LuaJIT version it is by doing: cd /usr/local/openresty/luajit/share/ and then ls. It will list a luajit folder like luajit-2.1.0-beta3, the suffix here is jit-2.1.0-beta3. If this isn't so, replace the suffix accordingly.

Then install Casbin's system dependencies by:

sudo apt update
sudo apt install gcc libpcre3 libpcre3-dev

NOTE: If you use yum you could use pcre and pcre-devel for PCRE.

Then install Casbin's latest current release using:

sudo /usr/local/openresty/luajit/bin/luarocks install casbin

NOTE: Here too the LuaRocks has its executable at /usr/local/openresty/luajit/bin/luarocks, if you have it installed somewhere else for OpenResty replace with that instead.

Usage

• Install lua-resty-casbin by LuaRocks:

sudo /usr/local/openresty/luajit/bin/luarocks install https://raw.githubusercontent.com/casbin-lua/lua-resty-casbin/master/lua-resty-casbin-1.0.0-1.rockspec

• In your conf/nginx.conf, initialize a CasbinMiddleware in the init_by_lua_block as (where authorizedRequest is a function which is called after a request is authorised):

e = CasbinMiddleware:new(authorizedRequest)

• Then in your content_by_lua_block, insert the command to check if the request is authorized everytime a request is sent (after you have authenticated):

e:check()

Example

You can try out an example of this by copying openresty_example directory to your system. Then to start the server:

cd openresty_example
sudo openresty -p $PWD/

This will start the server at http://127.0.0.1:8080/.

The current policy authz_policy.csv is:

p, *, /, GET
p, admin, *, *
g, alice, admin

This means that all users can access the homepage / but only users with admin permissions like alice can access other pages and other HTTP request methods.

For example, if you use:

curl --header "username: anonymous" 'http://127.0.0.1:8080/'

it will result in:

Authorized request

while,

curl --header "username: anonymous" 'http://127.0.0.1:8080/res1'

it will result in a 403 Forbidden page.

But if you send:

curl --header "username: alice" 'http://127.0.0.1:8080/res1'

it will result in:

Authorized request

since alice has admin permissions.

Documentation

The authorization determines a request based on {subject, object, action}, which means what subject can perform what action on what object. In this plugin, the meanings are:

1. subject: the logged-in username as passed in the header
2. object: the URL path for the web resource like "dataset1/item1"
3. action: HTTP method like GET, POST, PUT, DELETE, or the high-level actions you defined like "read-file", "write-blog" For how to write authorization policy and other details, please refer to the Casbin's documentation.

Example (without the middleware)

You can use Casbin without the middleware as per your authorization design, this is a sample example for that. You can create a lua module for OpenResty applications as shown here or add it to your existing lua module:

• In the file where you want to use Casbin, use local Enforcer = require("casbin") inside the content_by_lua_block. Here is a sample describing usage for basic model/policy and ABAC model/policy:

Basic model/policy example (nginx.conf file)

worker_processes 1;

events {
    worker_connections 1024;
}

http {
    lua_package_path "$prefix/lua/?.lua;;";

    server {
        listen 8080 reuseport;

        location / {
            default_type text/plain;
            content_by_lua_block {
                local Enforcer = require("casbin")
                local model  = "examples/basic_model.conf" -- The model file path
                local policy  = "examples/basic_policy.csv" -- The policy file path
                
                local e = Enforcer:new(model, policy) -- The Casbin Enforcer
                ngx.say("The result is:")
                ngx.say(e:enforce("alice", "data1", "read")) -- The enforce function with its arguments
            }
        }
    }
}

NOTE: To use this example, you need to create an examples directory at the top level of your application / along with the conf directory. And then copy the basic_model.conf and basic_policy.csv to that examples directory.

ABAC model/policy example (nginx.conf file)

worker_processes 1;

events {
    worker_connections 1024;
}

http {
    lua_package_path "$prefix/lua/?.lua;;";

    server {
        listen 8080 reuseport;

        location / {
            default_type text/plain;
            content_by_lua_block {
                local Enforcer = require("casbin")
                local model  = "examples/abac_rule_model.conf"
    		local policy  = "examples/abac_rule_policy.csv"
    		local sub1 = {
        		Name = "Alice",
        		Age = 16
    		}
    		local sub2 = {
        		Name = "Bob",
        		Age = 20
    		}
    		local sub3 = {
        		Name = "Alice",
        		Age = 65
    		}
    		local e = Enforcer:new(model, policy)
    		ngx.say("The result is:")
    		ngx.say(e:enforce(sub2, "/data1", "read"))
            }
        }
    }
}

NOTE: Similar to the former example to use this, you need to create an examples directory at the top level of your application / along with the conf directory. And then copy the abac_rule_model.conf and abac_rule_policy.csv to that examples directory.

Then use sudo openresty -p $PWD/ to start the server and use curl http://127.0.0.1:8080/ to fetch the page which for the above examples should output in:

The result is:
true

You can check other examples here and the Built-In Functions currently supported here.

Getting Help

• Casbin

License

This project is under the Apache 2.0 License.