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feature: allow client redirects via 302 responses (#3130) #3131

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This commit changes the behaviour of the webhook filter when a 302 Found response is received from the AuthN/AuthZ endpoint. As a result, it allows front-end facing (i.e. non-API) traffic to be filtered via the webhook.

Documentation updates and increased test coverage are included.

Incidental: Prevent the webhook client from following redirects from the AuthN/AuthZ endpoint: during testing I realised that the default net/http behaviour was in use - i.e. redirects were followed. Is this an intended behaviour of the filter: it's not documented, and it seems potentially risky?

Please take a look at #3130 for more details.


Changes:

  1. Update to the documentation - filters.md.
  2. Update to the auth reject() function, whereby the Location header is forwarded to the client if a 302 is encountered from the AuthN/AuthZ endpoint.
  3. Prevent the webhook filter from following 302 redirects.
  4. Update tests to cover 302 redirect forwarding.

This commit changes the behaviour of the webhook filter when a 302 Found
response is recieved from the AuthN/AuthZ endpoint. As a result, it allows
front-end facing (i.e. non-API) traffic to be filtered via the webhook.

Documentation updates and increased test coverage is included.

Incidental: Prevent the webhook client from following redirects from the
AuthN/AuthZ endpoint: during testing I realised that the default `net/http`
behaviour was in use - i.e. redirects were followed.

Signed-off-by: Fergus Morrow <[email protected]>
@FergusInLondon
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I'm more than happy to adapt or change the approach if required - especially if there's any reason why the webhook filter is expected to follow redirects itself.

Bringing the webhook filter closer to traefik's ForwardAuth functionality - i.e. having more control over the response returned to the client - would be very useful though!

@FergusInLondon FergusInLondon changed the title webhook filter: allow client redirects via 302 responses (#3130) feature: allow client redirects via 302 responses (#3130) Jun 28, 2024
@@ -133,12 +138,16 @@ func reject(
ctx.Serve(rsp)
}

func redirect(ctx filters.FilterContext, username string, reason rejectReason, destination, debuginfo string) {
reject(ctx, http.StatusFound, username, reason, "", debuginfo, destination)
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please provide the body of the function and not re-use redirect.
This will add a bit of code, but reduce the size of change.
reject should only be used for rejection as 4xx, thanks!

@@ -15,15 +15,17 @@ import (
)

const headerToCopy = "X-Copy-Header"
const webhookRedirectLocation = "https://example.com/auth"
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Please use: "https://redirect.example/auth" as by RFC this is in .example, so better than in .com.

@szuecs szuecs added the major moderate risk, for example new API, small filter changes that have no risk like refactoring or logs label Jul 2, 2024
@ppoloskov
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Any plans to merge this change?

@szuecs
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szuecs commented Dec 9, 2024

Any plans to merge this change?

Can you share your use case?
In my point of view it has a potential problem but also a useful change. In general who follows the redirect should not be an issue, but behavior change is always a higher risk factor.

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3 participants