Retrieving ASM Policy ID or md5hash without fetching entire ASM policy list

Depending on the version you should be able to use select and filter to only return the values you want.

Example using 'select':

curl -sku admin:admin https://${bigip_mgmt}/mgmt/tm/asm/policies?\$select=name,id | jq .

{
  "kind": "tm:asm:policies:policycollectionstate",
  "selfLink": "https://localhost/mgmt/tm/asm/policies?$select=name%2Cid&ver=13.1.0",
  "totalItems": 3,
  "items": [
    {
      "kind": "tm:asm:policies:policystate",
      "selfLink": "https://localhost/mgmt/tm/asm/policies/fAbyu1LnMcZ4DIMoZbX8aQ?ver=13.1.0",
      "name": "pabnagd_testing",
      "id": "fAbyu1LnMcZ4DIMoZbX8aQ"
    },
    {
      "kind": "tm:asm:policies:policystate",
      "selfLink": "https://localhost/mgmt/tm/asm/policies/qeho9K6GhLF0y7x7kShkHw?ver=13.1.0",
      "name": "Policy_1",
      "id": "qeho9K6GhLF0y7x7kShkHw"
    },
    {
      "kind": "tm:asm:policies:policystate",
      "selfLink": "https://localhost/mgmt/tm/asm/policies/1ClbVJ8ymjI19OMzkHeN2Q?ver=13.1.0",
      "name": "Policy_2",
      "id": "1ClbVJ8ymjI19OMzkHeN2Q"
    }
  ]
}

Example using 'filter' and 'select' to extract a specific policy:

curl -sku admin:admin https://${bigip_mgmt}/mgmt/tm/asm/policies?\$filter=name%20eq%20"Policy_1"\&\$select=name,id | jq .

{
  "kind": "tm:asm:policies:policycollectionstate",
  "selfLink": "https://localhost/mgmt/tm/asm/policies?$select=name%2Cid&ver=13.1.0&$filter=name%20eq%20Policy_1",
  "totalItems": 1,
  "items": [
    {
      "kind": "tm:asm:policies:policystate",
      "selfLink": "https://localhost/mgmt/tm/asm/policies/qeho9K6GhLF0y7x7kShkHw?ver=13.1.0",
      "name": "Policy_1",
      "id": "qeho9K6GhLF0y7x7kShkHw"
    }
  ]
}