HTTP parameter pollution canaries

Use two distinct benign values for a documented parameter to learn whether the edge, application, and downstream service choose first, last, merge, or reject duplicates.

Tags: hpp, parameters, api, authorized-testing

Controlled probes

```
?theme=CANARY-A&theme=CANARY-B
```
```
theme=CANARY-A&theme=CANARY-B
```

Observe only validation errors, reflected value, or an owned test record

Source: https://wstg.owasp.org/latest/4-Web_Application_Security_Testing/07-Injection/04-HTTP_Parameter_Pollution/

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HTTP parameter pollution canaries

Controlled probes

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