Remove user secret key from encrypted session token (#652)

User secret key is not really need it to be stored inside the encrypted
session key, since the `change-password` endpoint requires the user to
provide the current `secret key` that password will be used to
initialize a new minio client then we will leverage on the
`SetUser` operation, this api only works with actual user credentials
and not sts credentials

pkg/auth/token_test.go

@@ -36,14 +36,14 @@ func TestNewJWTWithClaimsForClient(t *testing.T) {
 	funcAssert := assert.New(t)
 	// Test-1 : NewEncryptedTokenForClient() is generated correctly without errors
 	function := "NewEncryptedTokenForClient()"
-	token, err := NewEncryptedTokenForClient(creds, "", "", []string{""})
+	token, err := NewEncryptedTokenForClient(creds, "", []string{""})
 	if err != nil || token == "" {
 		t.Errorf("Failed on %s:, error occurred: %s", function, err)
 	}
 	// saving token for future tests
 	goodToken = token
 	// Test-2 : NewEncryptedTokenForClient() throws error because of empty credentials
-	if _, err = NewEncryptedTokenForClient(nil, "", "", []string{""}); err != nil {
+	if _, err = NewEncryptedTokenForClient(nil, "", []string{""}); err != nil {
 		funcAssert.Equal("provided credentials are empty", err.Error())
 	}
 }