Switch permission checks to use a HashSet

[coderabbitai]

Description

The function currently uses a Vec to store and check allowed HTTP domains. This approach allows domains to be duplicated. While not likely to lead to issues, it's inelegant.

Suggestion

Switch the data structure from a Vec to a HashSet. This change is expected to reduce the complexity of the domain check from O(n) to O(1).

Benefits

• Slightly improved lookup performance for allowed HTTP domains.
• Avoid duplicated domain entries

Considerations

• Ensure compatibility and minimal impact on existing functionality.

This issue was prompted by a pull request review discussion: #253 (comment)