Add param pattern support

[blakeembrey]

Extremely simple version of #380, meant to be a starting point for more iteration on the actual regex allowed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (05a5a97) to head (b4fb596).

Additional details and impacted files

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##            master      #417   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files            1         1           
  Lines          369       418   +49     
  Branches       132       150   +18     
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+ Hits           369       418   +49     

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[bjohansebas]

Okay, the code looks good. Could you please update the README?

[Helveg]

Is it possible to also add other common valid URL characters like - _ ! $ & ' , ; = to the allowed characters? They seem completely innocent. Maybe even + (commonly used for spaces) and *, ?, I'm not sure they can do harm if ( ) are not allowed, perhaps they should only be allowed when they're explicitly escaped like \+, \*, \? ?

[blakeembrey]

Is it possible to also add other common valid URL characters like - _ ! $ & ' , ; = to the allowed characters?

Absolutely, this was just a scaffold to start iterating on but I can add them to the PR. One open question on ^ and $, since they're invalid in the regex output, is whether they should be escaped? I'm leaning toward yes and documenting the supported regex features/DSL in the README clearly.

Maybe even + (commonly used for spaces) and *, ?, I'm not sure they can do harm if ( ) are not allowed, perhaps they should only be allowed when they're explicitly escaped like +, *, ? ?

Depends on if we're supporting repeat/optional features. If so, yes, they'd need to be escaped. That's where using a regex to validate completely breaks down and, with repeats, a ReDoS vector opens so it's a more complex PR.