sts: allow clients to send certificate chain (#13235)

This commit fixes an issue in the `AssumeRoleWithCertificate`
handler.

Before clients received an error when they send
a chain of X.509 certificates (their client certificate as
well as intermediate / root CAs).

Now, client can send a certificate chain and the server
will only consider non-CA / leaf certificates as possible
client certificate candidates. However, the client still
can only send one certificate.

Signed-off-by: Andreas Auernhammer <hi@aead.dev>
This commit is contained in:
Andreas Auernhammer 2021-09-17 18:37:01 +02:00 committed by GitHub
parent 91567ba916
commit 1fc0e9a6aa
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@ -683,6 +683,24 @@ func (sts *stsAPIHandlers) AssumeRoleWithCertificate(w http.ResponseWriter, r *h
writeSTSErrorResponse(ctx, w, true, ErrSTSInsecureConnection, errors.New("No TLS connection attempt"))
return
}
// A client may send a certificate chain such that we end up
// with multiple peer certificates. However, we can only accept
// a single client certificate. Otherwise, the certificate to
// policy mapping would be ambigious.
// However, we can filter all CA certificates and only check
// whether they client has sent exactly one (non-CA) leaf certificate.
var peerCertificates = make([]*x509.Certificate, 0, len(r.TLS.PeerCertificates))
for _, cert := range r.TLS.PeerCertificates {
if cert.IsCA {
continue
}
peerCertificates = append(peerCertificates, cert)
}
r.TLS.PeerCertificates = peerCertificates
// Now, we have to check that the client has provided exactly one leaf
// certificate that we can map to a policy.
if len(r.TLS.PeerCertificates) == 0 {
writeSTSErrorResponse(ctx, w, true, ErrSTSMissingParameter, errors.New("No client certificate provided"))
return
@ -693,7 +711,7 @@ func (sts *stsAPIHandlers) AssumeRoleWithCertificate(w http.ResponseWriter, r *h
}
var certificate = r.TLS.PeerCertificates[0]
if !globalSTSTLSConfig.InsecureSkipVerify {
if !globalSTSTLSConfig.InsecureSkipVerify { // Verify whether the client certificate has been issued by a trusted CA.
_, err := certificate.Verify(x509.VerifyOptions{
KeyUsages: []x509.ExtKeyUsage{
x509.ExtKeyUsageClientAuth,