The behavior of x509.Verify changed in Go 1.10, which broke a test in CFSSL.

The previous behavior was that when the array of extended key usages in x509.VerifyOptions contains ExtKeyUsageClientAuth, then calling x509.Verify on a valid chain to a leaf certificate with the client certificate auth EKU set results in a valid response, which is the expected behavior. In Go 1.10, this behavior only works when x509.VerifyOptions only contains ExtKeyUsageClientAuth. If x509.VerifyOptions contains both ExtKeyUsageClientAuth and ExtKeyUsageServerAuth, then x509.Verify fails this check for leaf certificate with a client authentication usage.

Is there a new requirement for leaf certificates with Client Auth?

What version of Go are you using (go version)?

go 1.10

Steps to reproduce

The following test fails in cfssl 1.3 (https://github.com/cloudflare/cfssl/tree/1.3.0)
https://github.com/cloudflare/cfssl/blob/master/bundler/bundler_test.go#L914

Output in Go 1.10

go test -v -run TestBundlerClientAuth ./bundler/...
=== RUN   TestBundlerClientAuth
2018/02/27 14:45:30 [INFO] bundling certificate for
2018/02/27 14:45:30 [INFO] the anchoring root is O=Root CA,L=San Francisco,ST=California,C=US
2018/02/27 14:45:30 [INFO] bundling certificate for
--- FAIL: TestBundlerClientAuth (0.02s)
	bundler_test.go:925: {"code":1214,"message":"x509: certificate specifies an incompatible key usage: asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 1}"}
FAIL
FAIL	github.com/cloudflare/cfssl/bundler	0.034s