Formar NewKerberosClient comments acording to golang standad, added test for DisablePAFXFast

Signed-off-by: Ruben <ruben.vp8510@gmail.com>

kerberos_client.go

@@ -19,14 +19,9 @@ func (c *KerberosGoKrb5Client) CName() types.PrincipalName {
 	return c.Credentials.CName()
 }
 
-/*
-*
-* Create kerberos client used to obtain TGT and TGS tokens
-* used gokrb5 library, which is a pure go kerberos client with
-* some GSS-API capabilities, and SPNEGO support. Kafka does not use SPNEGO
-* it uses pure Kerberos 5 solution (RFC-4121 and RFC-4120).
-*
- */
+// NewKerberosClient creates kerberos client used to obtain TGT and TGS tokens.
+// It uses pure go Kerberos 5 solution (RFC-4121 and RFC-4120).
+// uses gokrb5 library underlying which is a pure go kerberos client with some GSS-API capabilities.
 func NewKerberosClient(config *GSSAPIConfig) (KerberosClient, error) {
 	cfg, err := krb5config.Load(config.KerberosConfigPath)
 	if err != nil {

kerberos_client_test.go

@@ -84,3 +84,27 @@ func TestCreateWithKeyTab(t *testing.T) {
 		t.Errorf("Expected error:%s, got:%s.", err, expectedErr)
 	}
 }
+
+func TestCreateWithDisablePAFXFAST(t *testing.T) {
+	kerberosConfig, err := krbcfg.NewConfigFromString(testdata.TEST_KRB5CONF)
+	if err != nil {
+		t.Fatal(err)
+	}
+	// Expect to try to create a client with keytab and fails with "o such file or directory" error
+	expectedErr := errors.New("open nonexist.keytab: no such file or directory")
+	clientConfig := NewConfig()
+	clientConfig.Net.SASL.Mechanism = SASLTypeGSSAPI
+	clientConfig.Net.SASL.Enable = true
+	clientConfig.Net.SASL.GSSAPI.ServiceName = "kafka"
+	clientConfig.Net.SASL.GSSAPI.Realm = "EXAMPLE.COM"
+	clientConfig.Net.SASL.GSSAPI.Username = "client"
+	clientConfig.Net.SASL.GSSAPI.AuthType = KRB5_KEYTAB_AUTH
+	clientConfig.Net.SASL.GSSAPI.KeyTabPath = "nonexist.keytab"
+	clientConfig.Net.SASL.GSSAPI.KerberosConfigPath = "/etc/krb5.conf"
+	clientConfig.Net.SASL.GSSAPI.DisablePAFXFAST = true
+
+	_, err = createClient(&clientConfig.Net.SASL.GSSAPI, kerberosConfig)
+	if err.Error() != expectedErr.Error() {
+		t.Errorf("Expected error:%s, got:%s.", err, expectedErr)
+	}
+}