How do I split and flatten this JSON document

[Jens M. Kofoed]

Hi

I have a JSON document with an array which I would like to split and
flatten.
In my example below key4 is an array containing 2 documents. I need to
split the record based on each document in the key4 array, so I end up with
multiple records. Where each new record has a copy of all keys except key4
which should be flatten into each own document.
{
key1:value1,
key2:value2,
key3: {
  key3a:value3a,
  key3b:value3b
}
key4: [
   {
      key4a1:value4a1,
      key4a2:value4a2
  },
  {
      key4b1:value4b1,
      key4b2:value4b2
  }
]
}

Should be like this:
Record 1
{
key1:value1,
key2:value2,
key3: {
  key3a:value3a,
  key3b:value3b
}
key4:{
   key4a1:value4a1,
   key4a2:value4a2
  }
}

Record 2
{
key1:value1,
key2:value2,
key3: {
  key3a:value3a,
  key3b:value3b
}
key4:{
   key4b1:value4b1,
   key4b2:value4b2
  }
}

Kind regards
Jens M. Kofoed