Add test simulating YubiKey v5.2.4

There are YubiKeys v5.2.4 where the attestation intermediate (f9)
does not have a basic constraint extension, so that certificate
is not marked as a CA. The test and CA in this commit imitates
that use case. Currently the test case returns an error as we
don't support it. But if we change the verification to support
this use case, the test should change accordingly.

acme/challenge_test.go

@@ -2774,3 +2774,97 @@ func Test_doStepAttestationFormat(t *testing.T) {
 		})
 	}
 }
+
+func Test_doStepAttestationFormat_noCAIntermediate(t *testing.T) {
+	ctx := context.Background()
+
+	// This CA simulates a YubiKey v5.2.4, where the attestation intermediate in
+	// the CA does not have the basic constraint extension. With the current
+	// validation of the certificate the test case bellow returns an error, if
+	// we change the validation to support this use case, the test case bellow
+	// should change..
+	//
+	// See https://github.com/Yubico/yubikey-manager/issues/522
+	ca, err := minica.New(minica.WithIntermediateTemplate(`{"subject": {{ toJson .Subject }}}`))
+	if err != nil {
+		t.Fatal(err)
+	}
+	caRoot := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: ca.Root.Raw})
+
+	makeLeaf := func(signer crypto.Signer, serialNumber []byte) *x509.Certificate {
+		leaf, err := ca.Sign(&x509.Certificate{
+			Subject:   pkix.Name{CommonName: "attestation cert"},
+			PublicKey: signer.Public(),
+			ExtraExtensions: []pkix.Extension{
+				{Id: oidYubicoSerialNumber, Value: serialNumber},
+			},
+		})
+		if err != nil {
+			t.Fatal(err)
+		}
+		return leaf
+	}
+
+	signer, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	if err != nil {
+		t.Fatal(err)
+	}
+	serialNumber, err := asn1.Marshal(1234)
+	if err != nil {
+		t.Fatal(err)
+	}
+	leaf := makeLeaf(signer, serialNumber)
+
+	jwk, err := jose.GenerateJWK("EC", "P-256", "ES256", "sig", "", 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	keyAuth, err := KeyAuthorization("token", jwk)
+	if err != nil {
+		t.Fatal(err)
+	}
+	keyAuthSum := sha256.Sum256([]byte(keyAuth))
+	sig, err := signer.Sign(rand.Reader, keyAuthSum[:], crypto.SHA256)
+	if err != nil {
+		t.Fatal(err)
+	}
+	cborSig, err := cbor.Marshal(sig)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	type args struct {
+		ctx  context.Context
+		prov Provisioner
+		ch   *Challenge
+		jwk  *jose.JSONWebKey
+		att  *AttestationObject
+	}
+	tests := []struct {
+		name    string
+		args    args
+		want    *stepAttestationData
+		wantErr bool
+	}{
+		{"fail no intermediate", args{ctx, mustAttestationProvisioner(t, caRoot), &Challenge{Token: "token"}, jwk, &AttestationObject{
+			Format: "step",
+			AttStatement: map[string]interface{}{
+				"x5c": []interface{}{leaf.Raw, ca.Intermediate.Raw},
+				"alg": -7,
+				"sig": cborSig,
+			},
+		}}, nil, true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := doStepAttestationFormat(tt.args.ctx, tt.args.prov, tt.args.ch, tt.args.jwk, tt.args.att)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("doStepAttestationFormat() error = %#v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("doStepAttestationFormat() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}