fix: reject newlines in redirect locations

[FrankChen021]

What changed

• Validate the fully constructed redirect target before placing it in the Location response header.
• Reject redirect targets containing literal carriage returns or line feeds with HTTP 400.
• Preserve ordinary redirects and percent-encoded %0D/%0A URL data.
• Add focused tests for normal, encoded, CR, and LF cases.

Why

RedirectFilter copied a URL derived from request data directly into the Location header. java.net.URL permits literal CR/LF characters, which could allow HTTP response splitting in servlet containers that do not reject them independently.

Impact

Legitimate redirect targets retain their exact URL representation. Requests that would produce a raw newline in the response header are rejected before the response status or header is set.

Validation

• mvn -ntp test -pl server -am -Dtest=org.apache.druid.server.http.RedirectFilterTest -Dsurefire.failIfNoSpecifiedTests=false -Pskip-static-checks -Dweb.console.skip=true -T1C
• mvn -ntp test -pl server -Dtest=org.apache.druid.server.http.RedirectFilterTest -Dweb.console.skip=true -Pskip-static-checks
• mvn -ntp checkstyle:check -pl server -Dweb.console.skip=true

[Copilot]

Pull request overview

This PR hardens RedirectFilter against HTTP response splitting by rejecting redirect Location header values that contain literal carriage return (\r) or line feed (\n) characters after the redirect URL is fully constructed.

Changes:

• Add CR/LF validation for the redirect target prior to setting the Location response header (returning HTTP 400 on invalid values).
• Preserve normal redirects and percent-encoded %0D/%0A sequences without decoding them.
• Add unit tests covering normal redirects, encoded newline sequences, and literal CR/LF rejection cases.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
server/src/main/java/org/apache/druid/server/http/RedirectFilter.java	Rejects redirect targets containing literal CR/LF before setting the Location header.
server/src/test/java/org/apache/druid/server/http/RedirectFilterTest.java	Adds tests for normal redirects, encoded newline preservation, and CR/LF rejection behavior.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

[FrankChen021]

I have reviewed the code for correctness, edge cases, concurrency, and integration risks; no issues found.

Reviewed 2 of 2 changed files.

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This is an automated review by Codex GPT-5.6-Sol