What belongs in an Angular HTTP interceptor?

Uses functional interceptors for cross-cutting transport concerns without hiding domain behavior or unsafe retries.

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TL;DR

I use an interceptor for consistent transport concerns such as attaching an access token, correlation metadata, normalized logging, or mapping a shared authentication failure. Current Angular guidance favors functional interceptors because their behavior is more predictable in complex setups. Feature-specific decisions and user messages stay in the owning service or component.

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Angular HttpClient, functional interceptors, authentication, retries, errors, logging, and request immutability.

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Core answer
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Overview
Interceptors are transport middleware; they should handle cross-cutting request behavior, not absorb feature workflows.
I use an interceptor for consistent transport concerns such as attaching an access token, correlation metadata, normalized logging, or mapping a shared authentication failure. Current Angular guidance favors functional interceptors because their behavior is more predictable in complex setups. Feature-specific decisions and user messages stay in the owning service or component.
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Stronger answer
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Angular requests are immutable, so an interceptor clones a request when changing headers or context and then passes it to the next handler. Interceptor order matters because they form a chain, especially for timing, retries, and error mapping. I never log secrets or full sensitive payloads, and I retry only operations whose semantics make retry safe. A broad catch that converts every failure into one generic error would erase information the feature needs.

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Details

Putting feature navigation and UI messaging into a global interceptor.
Retrying every failed request, including non-idempotent commands.
Logging authorization headers or sensitive bodies.

What belongs in an Angular HTTP interceptor?

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