err    error
	)
	if c.signingKey != nil {
		// Initialize the signer only in the tests that make use of it.  We can
		// not defer this initialization because the test server uses it too.
		signer, err = jose.NewSigner(jose.SigningKey{
			Algorithm: jose.SignatureAlgorithm(c.signingKey.Algorithm),
			Key:       c.signingKey,
		}, nil)
		if err != nil {
			t.Fatalf("initialize signer: %v", err)
		}
	}