[SDK-2259] Remove env var dependency at build time

[adamjmcgrath]

Description

Because of static generation withPageAuthRequired is called at build time. We need to move the dependency withPageAuthRequired has on the server instance to be at runtime, so that you don't need to specify environment variables to configure the SDK at build time

References

fixes: #154

Testing

• This change adds test coverage for new/changed/fixed functionality

Checklist

• I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not master

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[StianOvrevage]

Is there a chance of getting this merged into main branch?