Create API keys on ElasticSearch with limited search capabilities - elasticsearch

Question

I want to create API keys on elasticsearch via POST _security/api_key API, I am able to create these but I want to limit search capability for the generated key which I am unable to do.
Essentially, what I want to achieve is let's say that all my records have a field like "username":"username1" or another one like "username":"username2" i.e. all the records will have a valid value for username field
Now what I want is to be able to create a key where I specify something like "username":"username2" which then gets appended to every search query made using that key as an AND case like if this key searches (/index_name/_search) for
{
"query": {
"match": {
"key_zz":"value_aa"
}
}
}
this query would actually be an AND of both of the below (i.e. if a record with this combination exists "key_zz":"value_aa" but the value for username is not username2, the API would not return that object)
{
"query": {
"match": {
"key_zz":"value_aa"
}
}
}
AND
{
"query": {
"must": {
"match" : {
"username":"username2"
}
}
}
}
I have tried creating the key with all of the following combinations:
"name": "key-name",
"role_descriptors": {
"role_name": {
"indices": [
{
"names": [
"index_name"
],
"privileges": [
"read"
],
"query": {
"match": {
"username": "value_custom"
}
}
}
]
}
}
}
In the query field, I have tried all the following combinations:
"query": {
"and": {
"username": "value_custom"
}
}
"query": {
"bool": {
"must": {
"match": {
"username": "value_custom"
}
}
}
}
"query": {
"bool": {
"must": {
"bool": {
"must": {
"match": {
"username": "value_custom"
}
}
}
}
}
}
But none of the above worked. Also, earlier the mapping type of username field was text but I then updated it to be keyword
In a nutshell, what I am trying to achieve is some kind of document level security. I know ElasticSearch has some kind of Document Level Security (https://www.elastic.co/guide/en/elastic-stack-overview/current/document-level-security.html) but in our architecture, we want to achieve this using API keys with restricted search capabilities. We are currently using Algolia and we were achieving this using the exact implementation I described above. ElasticSearch documentation has references for how to limit a role but not how to limit API keys. Need help to achieve this.
Also, I am using ElasticSearch v7
Some reference links :
https://www.elastic.co/guide/en/elasticsearch/reference/current/security-api-create-api-key.html
https://www.elastic.co/guide/en/elasticsearch/reference/current/security-api-put-role.html