JSON Schema: Conditionally require property depending on several properties' values - jsonschema

Question

I want to validate a JSON file using JSON schema, several "properties" should be required depending on what values some other properties have.
Example
Having properties "A", "B", "C", and "D"
if "A" has value "foo", C is required
if "B" has value "foo", D is required
if both "A" and "B" each have value "foo", both C and D are required
else, nothing is required
I have seen a very helpful answer here: https://stackoverflow.com/a/38781027/5201771 --> there, the author addresses how to solve this problem for the case of a single property (e.g., only "A" has value "foo", so require "C").
However, I currently don't see how to extend that answer to my case, where several properties determine the outcome.
Example Files
for illustration, I supply some files that should pass or fail the validation:
should pass:
{
"A": "bar"
"B": "baz"
}
{
"A": "foo"
"C": "some value"
}
{
"A": "bar"
"B": "foo"
"D": "some value"
}
should fail:
{
"A": "foo"
"B": "foo"
"D": "some value"
}

Answer 1

You can combine conditionals a number of ways, but combining them with allOf is usually the best way.
{
"type": "object",
"properties": {
"A": {},
"B": {},
"C": {},
"D": {}
},
"allOf": [
{ "$ref": "#/definitions/if-A-then-C-is-required" },
{ "$ref": "#/definitions/if-B-then-D-is-required" }
],
"definitions": {
"if-A-then-C-is-required": {
"if": {
"type": "object",
"properties": {
"A": { "const": "foo" }
},
"required": ["A"]
},
"then": { "required": ["C"] }
},
"if-B-then-D-is-required": {
"if": {
"type": "object",
"properties": {
"B": { "const": "foo" }
},
"required": ["B"]
},
"then": { "required": ["D"] }
}
}
}