Find user by user external ID

Example response

{
  "_links": [
    {
      "href": "https://an.example.link",
      "method": "GET",
      "rel": "self"
    }
  ],
  "email": "user@somegovernmentdept.gov.uk",
  "external_id": "93ba1ec4ed6a4238a59f16ad97b4fa12",
  "features": "feature1, feature2",
  "last_logged_in_at": "2022-04-06T23:03:41.665Z",
  "otp_key": "43c3c4t",
  "provisional_otp_key": "FC5IHFH2CFSKEZBBXTYEGQXQOH344LLO",
  "second_factor": "SMS",
  "service_roles": [
    {
      "role": {
        "description": "Administrator",
        "name": "admin",
        "permissions": [
          {
            "description": "Revokekey",
            "name": "tokens:delete"
          }
        ]
      },
      "service": {
        "_links": [
          {
            "href": "https://an.example.link",
            "method": "GET",
            "rel": "self"
          }
        ],
        "archived_date": "2023-04-09T18:07:46.568Z",
        "collect_billing_address": true,
        "created_date": "2022-04-01T12:07:46.568Z",
        "current_go_live_stage": "NOT_STARTED",
        "current_psp_test_account_stage": "NOT_STARTED",
        "custom_branding": {
          "css_url": "css url",
          "image_url": "image url"
        },
        "default_billing_address_country": "GB",
        "external_id": "7d19aff33f8948deb97ed16b2912dcd3",
        "gateway_account_ids": [
          "1"
        ],
        "merchant_details": {
          "address_city": "London",
          "address_country": "GB",
          "address_line1": "Address line 1",
          "address_line2": "Address line 2",
          "address_postcode": "E1 8XX",
          "email": "email@example.com",
          "name": "organisation name",
          "telephone_number": "447700900000",
          "url": "http://www.example.org"
        },
        "name": "Some service name",
        "sector": "local government",
        "service_features": {
          "test_feature": {
            "enabled": true
          },
          "test_feature_2": {
            "enabled": false
          }
        },
        "service_name": {
          "cy": "Service name in welsh",
          "en": "Some service name"
        },
        "went_live_date": "2022-04-09T18:07:46.568Z"
      }
    }
  ],
  "telephone_number": "447700900000"
}