Obtain an error if a Json contains key not defined in Constraints

[antimoroma]

I don't know, if is correct to ask this as a feature, or if is already present and i miss it,but if i have an object with:

{
  "a" : "aValue"
}

Define a constraints with:

val constraints =  {
  a : {
       presence  : true
 }

Is possible to have an error if i try to call validate with an Object like:

{
  "a"      : "aValue",
  "foo"   :  "sample"
}

because foo is not present in the constraints?
I know is easy , only to be sure that is not already present in the library (more simple than redefine all field) as in this example
https://stackoverflow.com/questions/54881865/check-if-multiple-keys-exists-in-json-object

May be i miss something in the doc , or is not a valid feature for the validation, anyway thank you :)