CORS: Why Is the Browser Blocking Me?

Questions

1. 1
   Not answered. Are these two URLs same-origin?
2. 2
   Not answered. How are https://app.example.com and https://api.example.com related?
3. 3
   Not answered. What does CORS control?
4. 4
   Not answered. A form-style cross-origin POST changes server state, but the response has no CORS headers. What happens?
5. 5
   Not answered. Which changes would trigger a CORS preflight?
6. 6
   Not answered. Which cross-origin requests can avoid a CORS preflight?
7. 7
   Not answered. Which request matches the preflight for a PATCH with Content-Type and X-Trace-Id?
8. 8
   Not answered. Will a CORS preflight include the user's session cookie?
9. 9
   Not answered. Can 204 No Content be a successful preflight response?
10. 10
    Not answered. Your auth middleware returns 401 for every unauthenticated OPTIONS request. How should you fix it?
11. 11
    Not answered. A preflight succeeds, then the actual PATCH returns 500 without Access-Control-Allow-Origin. What can browser JavaScript observe?
12. 12
    Not answered. Why might clearing the normal HTTP cache leave a preflight result cached?
13. 13
    Not answered. Why does Access-Control-Allow-Origin: * fail for fetch(url, { credentials: "include" })?
14. 14
    Not answered. Which response header pair can share a credentialed response with a page at https://app.example.com?
15. 15
    Not answered. Will Access-Control-Allow-Credentials: True authorize a credentialed CORS response?
16. 16
    Not answered. Is Access-Control-Allow-Origin: https://a.example, https://b.example a valid two-origin allowlist?
17. 17
    Not answered. Which cache header should you send when Access-Control-Allow-Origin changes with the request's Origin?
18. 18
    Not answered. Why is it dangerous to copy any request Origin into Access-Control-Allow-Origin when credentials are enabled?
19. 19
    Not answered. What is the default credentials mode for fetch("https://api.other.example/data")?
20. 20
    Not answered. What does credentials: "include" guarantee for a cross-site cookie?
21. 21
    Not answered. Can the browser accept Set-Cookie even when CORS prevents JavaScript from reading the response?
22. 22
    Not answered. Does Access-Control-Allow-Headers: * allow an Authorization request header?
23. 23
    Not answered. The Network panel shows X-Request-Id: abc, but response.headers.get("X-Request-Id") returns null. What is missing?
24. 24
    Not answered. Can frontend JavaScript read Set-Cookie by asking the server to send Access-Control-Expose-Headers: Set-Cookie?
25. 25
    Not answered. What numeric status does JavaScript observe on an opaque response?
26. 26
    Not answered. What can JavaScript read from a successful cross-origin JSON response fetched with mode: "no-cors"?
27. 27
    Not answered. Can a no-cors request have server-side effects even though JavaScript receives an opaque response?
28. 28
    Not answered. Why can't a rejected fetch() promise reliably distinguish a CORS failure from a network failure?
29. 29
    Not answered. What does "it works in the Postman desktop app" prove about a browser CORS failure?
30. 30
    Not answered. Will a SameSite=Lax session cookie accompany a cross-site fetch() POST from another site?
31. 31
    Not answered. When can a SameSite=Lax cookie be sent from a cross-site context?
32. 32
    Not answered. What happens to Set-Cookie: session=abc; SameSite=None when the Secure attribute is absent?
33. 33
    Not answered. A page on https://app.example.com fetches https://api.example.com. Which statements are true?
34. 34
    Not answered. Can a browser withhold a cross-site cookie even when Fetch, SameSite, Secure, and CORS are configured correctly?
35. 35
    Not answered. What protection does HttpOnly provide for a session cookie?
36. 36
    Not answered. Why do cookie-authenticated endpoints still need CSRF protection when their CORS policy is strict?
37. 37
    Not answered. Why does the page's inline script fail under Content-Security-Policy: script-src 'self'?
38. 38
    Not answered. Which change allows this inline bootstrap script under CSP?
39. 39
    Not answered. Why should a CSP nonce not be a constant copied into every response?
40. 40
    Not answered. Why can one extra space break a CSP hash for an inline script?
41. 41
    Not answered. The API returns correct CORS headers, but the page has Content-Security-Policy: connect-src 'self'. Why does the fetch still fail?
42. 42
    Not answered. What does Content-Security-Policy: default-src 'self' imply for a cross-origin fetch() when no connect-src is present?
43. 43
    Not answered. How can you test a proposed CSP without enforcing it?
44. 44
    Not answered. Which limits apply when CSP is delivered through a <meta> element?