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Course Library · Lesson 3 of 6
Digital · Guided lesson

Reject credentials and explain destination uncertainty

About 19 minutes · 4 reading + 15 practice and checks
Time includes reading, practice, and questions. Extra videos or further study are optional.
See this course’s project requirements

A defensive local link-directory app with text-only rendering, allowed URL schemes, same-origin explanation and a validation matrix using inert fictional strings.

Keep your working files in your own notebook or software. Save a private description, checklist, and work link in My Proof.

What to include

  • Demonstrate literal rendering of markup-like label text using fixed DOM structure.
  • Produce a parser-versus-policy matrix for accepted HTTPS and rejected scheme/relative cases.
  • Show embedded-credential rejection and distinguish address validation from destination review.
  • Create an origin tuple comparison and a correct browser-access boundary explanation.
  • Retain inert validation tests, literal-render observations, and unchanged-list rejection evidence.
  • Deliver the tested local directory with explicit implemented rules and unimplemented security boundaries.

Review and revise

Use these criteria to check your work and choose what to improve.

  • The implementation or declared simulation follows the supplied contract and retains inspectable original inputs.
  • Normal, boundary and rejected cases are recorded with expected versus observed results.
  • The changed case has a correct explanation and does not rely on hidden state.
  • The project includes source, outputs, instructions and honest tool, privacy and verification limits.
Open the full course project
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Before you begin

The idea in everyday life

Use directory.html, link-rules.mjs and test-links.mjs with label <b>Guide</b> and https://example.com/help. Serve locally with python3 -m http.server 8765 --bind 127.0.0.1. The markup-like label is inert text; do not follow external links during practice.

The idea

Credentials embedded in a URL are excluded by this policy. HTTPS protects a transport context but does not certify the destination’s content or honesty.

Follow along

Reject credentials and explain destination uncertainty — original worked practice

Credentials embedded in a URL are excluded by this policy. HTTPS protects a transport context but does not certify the destination’s content or honesty.

Use directory.html, link-rules.mjs and test-links.mjs with label <b>Guide</b> and https://example.com/help. Serve locally with python3 -m http.server 8765 --bind 127.0.0.1. The markup-like label is inert text; do not follow external links during practice.

  1. 1. Step 1

    Try https://name:fake@example.com in the input without activating it.

    You should see: The credential-bearing URL is rejected.

    Credentials embedded in a URL are excluded by this policy. HTTPS protects a transport context but does not certify the destination’s content or honesty.

  2. 2. Step 2

    Inspect u.username and u.password checks.

    You should see: Both embedded credential fields are disallowed.

    Credentials embedded in a URL are excluded by this policy. HTTPS protects a transport context but does not certify the destination’s content or honesty.

  3. 3. Step 3

    Add the harmless HTTPS example and read the status about unverified destination content.

    You should see: Scheme validation does not claim destination approval.

    Credentials embedded in a URL are excluded by this policy. HTTPS protects a transport context but does not certify the destination’s content or honesty.

  4. 4. Step 4

    Write a two-column distinction: validated components versus unverified destination claims.

    You should see: A URL component and uncertainty record.

    Credentials embedded in a URL are excluded by this policy. HTTPS protects a transport context but does not certify the destination’s content or honesty.

Now change one thing

https://example.com parses with no credentials. Does that prove its page information is accurate?

Your work

What to finish

Show embedded-credential rejection and distinguish address validation from destination review.

Common mistake

Watch for this

Labeling an HTTPS URL safe or trusted solely because its scheme passed.

How can I tell I understand it?

Demonstrate the rule: Credentials embedded in a URL are excluded by this policy. HTTPS protects a transport context but does not certify the destination’s content or honesty. Use the supplied variant to distinguish a changed result from a broken implementation.

Try 3 questions

Quick knowledge check

Answer all 3 questions. Get at least 2 right and the lesson completes automatically.

Not yet passed

You’ll get an explanation for each answer. Signed in? Your results save to your account.

1Why reject https://name:fake@example.com here?
2What does the accepted HTTPS scheme fail to establish?
3Which status statement is accurate after a local accepted URL?
0 of 3 answeredApply the lesson to a short question, then review the explanation.
3
Finish this lesson

Pass the check. We’ll save the progress.

Answer all 3 questions above and get at least 2 right. You can review the explanations and try again.

Go to the knowledge check
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Sources and further reading

Explore the references behind this lesson.

developer.mozilla.org — URL
Source & access notes · checked 2026-10-01

Relevant documented module/API behavior inspected during expansion authoring; actual execution evidence is recorded separately. No grant eligibility is established.

Access: Official page retrieved with the web reader on 2026-10-01. Documentation reading does not certify execution in every native tool or browser.

Reuse: Original local practice files, fictional data, worked examples and questions. Concepts paraphrased and linked; source exercises are not copied.

developer.mozilla.org — Same origin_policy
Source & access notes · checked 2026-10-01

Relevant documented module/API behavior inspected during expansion authoring; actual execution evidence is recorded separately. No grant eligibility is established.

Access: Official page retrieved with the web reader on 2026-10-01. Documentation reading does not certify execution in every native tool or browser.

Reuse: Original local practice files, fictional data, worked examples and questions. Concepts paraphrased and linked; source exercises are not copied.

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