Name
    Plack::Middleware::CSP - Apply HTTP::CSPHeader to your psgi application.

Synopsis
     use utf8;
     use strict;
     use warnings;
     use Plack::Builder;
     use Plack::Middleware::CSP;

     my $app = sub {
         my $env = shift;
         [ 200,
           [ "content-type" => "text/plain; charset=utf-8" ],
           [ "OHAI $env->{CSP_NONCE}" ] ]
     };

     # CSP middleware takes the arguments for HTTP::CSPHeader.
     builder {
         enable "CSP" =>
             policy => {
                 'default-src' => q['self'],
                 'script-src'  => q['self'],
             }, nonces_for => 'script-src';

         mount "/" => $app;
     };

    Test it–

     plackup app.psgi

    See the headers–

     curl -I http://0:5000/

  policy, nonces_for
    Refer to HTTP::CSPHeader’s documentation.

  $env->{CSP_NONCE}
    The nonce for the response is in the psgi environment as CSP_NONCE.

  nonce_template_token
    There is an experimental feature to do automatic nonce substitutions in
    the response body, for example in a template. It is experimental because
    it might be a terrible idea and even if it's a good idea, it almost
    certainly needs to be much less liberal with its approach. It should
    probably require the calling code to declare target content type. Adding
    it into our synopsis–

     use utf8;
     use strict;
     use warnings;
     use Plack::Builder;
     use Plack::Middleware::CSP;

     my $app = sub { [ 200,
                      [ "content-type" => "text/plain; charset=utf-8" ],
                      [ "DIS IZ MAI NONCE: ::nonce::!" ] ] };

     builder {
         enable "CSP" =>
             nonce_template_token => "::nonce::",
             policy => {
                 'default-src' => q['self'],
                 'script-src'  => q['self'],
             }, nonces_for => 'script-src';

         mount "/" => $app;
     };

RFC
    I put this together just to work on some security testing for myself.
    It's alpha, unreviewed code, only tested on simplistic cases. It almost
    certainly has bugs.

    Please submit any patches, tests, feedback, or issues through its repo,
    <https://github.com/pangyre/Plack-Middleware-CSP/issues>.

See Also
    The excellent Leon Timmermans took a stab at this quite a few years ago:
    <https://github.com/Leont/plack-middleware-csp>. I have not made any
    tests or comparisons.

    HTTP::CSPHeader, Plack, Plack::Middleware, Plack::Util.

    <https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP>.

Author
    Ashley Pond V, "<ashley@cpan.org>".

License
    ©2022 Ashley Pond V. This program is free software; you can redistribute
    it and modify it under the same terms as Perl itself.

    See <http://dev.perl.org/licenses/artistic.html>.