Add Content-Security-Policy Default directives as found in Helmet

[offgriddev]

🌱 Feature Request

Is your feature request related to a problem? Please describe.

As a solution similar to helmet, it would be beneficial for consumers to have similar defaults, so as to align with other packages features. This would provide consumers with a simple interface to match other packages leveraging helmet defaults. Otherwise, consumers need to specify these in their repositories.

You can find the defaults in helmet here

Describe the solution you'd like

Somewhere in the CSP rule, you could allow users to specify they want a set of default directives here: https://github.com/jagaapple/next-secure-headers/blob/master/src/rules/content-security-policy.ts#L226-L238

The behavior of the helmet repository is that if you tell it to include CSP without specifying any directives, it will default to the set defined in the module here

next-secure-headers can implement something similar by here:
https://github.com/jagaapple/next-secure-headers/blob/master/src/rules/content-security-policy.ts#L213-L223

When no directives are passed through, it can default to the same set of directives.

Describe alternatives you've considered

Consumers need to maintain a basic set of default directives for helmet independently when this should rest with the package.

Documentation, Adoption, Migration Strategy

If you can, explain how users will be able to use this and how it might be documented. Maybe a mock-up?

Additional context

Add any other context or screenshots about the feature request here.

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• I've tried to find similar issues and pull requests
• I would like to work on this feature 💪🏻

[offgriddev]

It's important to point out here that there are defaults available on createSecureHeaders() here, but nothing for Content-Security-Policy. While CSP has side-effects due to the restrictions it places on loading resources, the default directives defined in the helmet repository are reasonable as a baseline, so someone coming in wanting to get some basic protections can use the defaults and build on top of them. The default directives in helmet can be found here