Implement ABAC

[xcaptain]

#78 Because rust doesn't support variadic parameters, we finally decide to use a json string to represent a request object, it can be parsed into a json object and then do evaluation in rhai.

@GopherJ please take a look

@schungx I found #{} works in 0.11.1, so no need to upgrade to 0.12.0 right?

[codecov]

Codecov Report

Merging #102 into master will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #102      +/-   ##
==========================================
+ Coverage   86.41%   86.45%   +0.03%     
==========================================
  Files          20       20              
  Lines        2841     2849       +8     
==========================================
+ Hits         2455     2463       +8     
  Misses        386      386              

Impacted Files	Coverage Δ
src/enforcer.rs	91.64% <100.00%> (ø)
src/model/default_model.rs	95.28% <100.00%> (+0.07%)	⬆️
src/util.rs	100.00% <0.00%> (ø)

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[schungx]

@schungx I found #{} works in 0.11.1, so no need to upgrade to 0.12.0 right?

That's correct. Object maps work in 0.11.1. I'll put out a 0.12.0 soon.

[schungx]

let scope_exp = format!("let {} = \"{}\";", token, rvals[i].as_ref());
engine.eval_with_scope::<()>(&mut scope, &scope_exp)?;

This is not necessary and you run the risk of not properly sanitizing your input (e.g. if rval[i] contains a quote character).

I'd suggest something like this:

scope.push_constant(token, rvals[i].clone());

assuming rvals[i] is a String.

[xcaptain]

Thanks, push_constant is much more secure then write an assignment statement and then eval_with_scope. After rhai 0.12.0 released we can then eval a json object directly without need to write const {} = #{};

@GopherJ Since json string is usually derived from a struct, so we are less likely to see sanitize problems here, I think we can keep this style first and when parse_json get stable then migrate to the new style.

[GopherJ]

I agree maybe we don't need to validate, rhai will return an error if it's not the correct format

[schungx]

I agree maybe we don't need to validate, rhai will return an error if it's not the correct format

True... Rhai is sandboxed meaning that you can't really harm the system other than getting a syntax error.

[GopherJ]

thanks @xcaptain