Allow App Custom Fields to be set using their Value via JSON

Currently custom field created using app rest api  can only be set using their ID and not value. 

Working Example:

 {
 "fields": 
{ 
"customfield_xxxx": <id>
}
} 

Non-working Example:

  { 
"fields": 
{ "customfield_xxxx": "<value>"
 }
 } 

It will be helpful if app custom fields can also be edited using their values.