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Support RFC-9440 colon-wrapped Base64 for forwarded client certs #31501

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b757b34
Add support for RFC 9440/8941 structured headers in client certificat…
husunal Aug 15, 2025
7c6d774
Add changelog
husunal Aug 27, 2025
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81 changes: 81 additions & 0 deletions http/forwarded_for_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -334,6 +334,87 @@ func TestHandler_XForwardedFor(t *testing.T) {
t.Fatalf("bad body: %v vs %v", buf.String(), testcertificate)
}
})

// Test RFC 9440/8941 Structured Headers "byte sequence" format
t.Run("pass_cert_rfc9440_format", func(t *testing.T) {
t.Parallel()
testHandler := func(props *vault.HandlerProperties) http.Handler {
origHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
w.WriteHeader(http.StatusOK)
w.Write([]byte(base64.StdEncoding.EncodeToString(r.TLS.PeerCertificates[0].Raw)))
})
listenerConfig := getListenerConfigForMarshalerTest(goodAddr)
listenerConfig.XForwardedForClientCertHeader = "X-Forwarded-Tls-Client-Cert"
listenerConfig.XForwardedForClientCertHeaderDecoders = "BASE64"
return WrapForwardedForHandler(origHandler, listenerConfig)
}

cluster := vault.NewTestCluster(t, nil, &vault.TestClusterOptions{
HandlerFunc: HandlerFunc(testHandler),
})
cluster.Start()
defer cluster.Cleanup()
client := cluster.Cores[0].Client

req := client.NewRequest("GET", "/")
req.Headers = make(http.Header)
req.Headers.Set("x-forwarded-for", "5.6.7.8")
// Test certificate in RFC 9440/8941 format with leading and trailing colons
testcertificate := `: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:`
req.Headers.Set("x-forwarded-tls-client-cert", testcertificate)
resp, err := client.RawRequest(req)
if err != nil {
t.Fatal(err)
}
defer resp.Body.Close()
buf := bytes.NewBuffer(nil)
buf.ReadFrom(resp.Body)
// Strip the colons for comparison
expectedCert := testcertificate[1 : len(testcertificate)-1]
if !strings.Contains(buf.String(), expectedCert) {
t.Fatalf("bad body: %v vs %v", buf.String(), expectedCert)
}
})

// Test that regular base64 without colons still works for compatibility
t.Run("pass_cert_regular_base64", func(t *testing.T) {
t.Parallel()
testHandler := func(props *vault.HandlerProperties) http.Handler {
origHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
w.WriteHeader(http.StatusOK)
w.Write([]byte(base64.StdEncoding.EncodeToString(r.TLS.PeerCertificates[0].Raw)))
})
listenerConfig := getListenerConfigForMarshalerTest(goodAddr)
listenerConfig.XForwardedForClientCertHeader = "X-Forwarded-Tls-Client-Cert"
listenerConfig.XForwardedForClientCertHeaderDecoders = "BASE64"
return WrapForwardedForHandler(origHandler, listenerConfig)
}

cluster := vault.NewTestCluster(t, nil, &vault.TestClusterOptions{
HandlerFunc: HandlerFunc(testHandler),
})
cluster.Start()
defer cluster.Cleanup()
client := cluster.Cores[0].Client

req := client.NewRequest("GET", "/")
req.Headers = make(http.Header)
req.Headers.Set("x-forwarded-for", "5.6.7.8")
// Regular base64 without URL encoding and without colons
testcertificate := `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`
req.Headers.Set("x-forwarded-tls-client-cert", testcertificate)
resp, err := client.RawRequest(req)
if err != nil {
t.Fatal(err)
}
defer resp.Body.Close()
buf := bytes.NewBuffer(nil)
buf.ReadFrom(resp.Body)
if !strings.Contains(buf.String(), testcertificate) {
t.Fatalf("bad body: %v vs %v", buf.String(), testcertificate)
}
})

t.Run("reject invalid IP", func(t *testing.T) {
t.Parallel()
testHandler := func(props *vault.HandlerProperties) http.Handler {
Expand Down
9 changes: 8 additions & 1 deletion http/handler.go
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Original file line number Diff line number Diff line change
Expand Up @@ -671,7 +671,14 @@ func WrapForwardedForHandler(h http.Handler, l *configutil.Listener) http.Handle
}
v = decoded
case "BASE64":
decoded, err := base64.StdEncoding.DecodeString(v)
// Support RFC 9440/8941 Structured Headers byte sequence values (":MIIC...==:").
// If the value is wrapped in leading/trailing colons, unwrap before decoding.
base64Value := v
if len(v) >= 2 && v[0] == ':' && v[len(v)-1] == ':' {
base64Value = v[1 : len(v)-1]
}

decoded, err := base64.StdEncoding.DecodeString(base64Value)
if err != nil {
respondError(w, http.StatusBadRequest, fmt.Errorf("failed to base64 decode the client certificate: %w", err))
return
Expand Down
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