curl --request GET \
  --url https://api.onesignal.com/apps/{app_id}/users/by/{alias_label}/{alias_id}/identity \
  --header 'Authorization: <authorization>'

import Onesignal from '@onesignal/node-onesignal';

const configuration = Onesignal.createConfiguration({
    restApiKey: 'YOUR_REST_API_KEY',
});
const apiInstance = new Onesignal.DefaultApi(configuration);

// string
const appId: string = "00000000-0000-0000-0000-000000000000";
// string
const aliasLabel: string = "external_id";
// string
const aliasId: string = "YOUR_USER_EXTERNAL_ID";

try {
  const response = await apiInstance.getAliases(appId, aliasLabel, aliasId);
  console.log(response);
} catch (e) {
  if (e instanceof Onesignal.ApiException) {
    // `e.errorMessages` flattens any error-envelope shape to a `string[]`;
    // the raw parsed body remains on `e.body`.
    console.error("getAliases failed: HTTP " + e.code, e.errorMessages);
  } else {
    throw e;
  }
}

import onesignal
from onesignal.api import default_api
from onesignal.models import *
from pprint import pprint

# See configuration.py for a list of all supported configuration parameters.
# Some of the OneSignal endpoints require ORGANIZATION_API_KEY token for authorization, while others require REST_API_KEY.
# We recommend adding both of them in the configuration page so that you will not need to figure it out yourself.
configuration = onesignal.Configuration(
    rest_api_key = "YOUR_REST_API_KEY", # App REST API key required for most endpoints
    organization_api_key = "YOUR_ORGANIZATION_API_KEY" # Organization key is only required for creating new apps and other top-level endpoints
)


# Enter a context with an instance of the API client
with onesignal.ApiClient(configuration) as api_client:
    # Create an instance of the API class
    api_instance = default_api.DefaultApi(api_client)
    app_id = "00000000-0000-0000-0000-000000000000" 
    alias_label = "external_id" 
    alias_id = "YOUR_USER_EXTERNAL_ID" 

    try:
        api_response = api_instance.get_aliases(app_id, alias_label, alias_id)
        pprint(api_response)
    except onesignal.ApiException as e:
        print("Exception when calling DefaultApi->get_aliases: %s\n" % e)
        print("Status Code: %s" % e.status)
        print("Response Body: %s" % e.body)

<?php
require_once(__DIR__ . '/vendor/autoload.php');


// Configure Bearer authorization: rest_api_key
$config = onesignal\client\Configuration::getDefaultConfiguration()
                                                ->setRestApiKeyToken('YOUR_REST_API_KEY')
                                                ->setOrganizationApiKeyToken('YOUR_ORGANIZATION_API_KEY');



$apiInstance = new onesignal\client\Api\DefaultApi(
    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
    // This is optional, `GuzzleHttp\Client` will be used as default.
    new GuzzleHttp\Client(),
    $config
);
$app_id = '00000000-0000-0000-0000-000000000000'; // string
$alias_label = 'external_id'; // string
$alias_id = 'YOUR_USER_EXTERNAL_ID'; // string

try {
    $result = $apiInstance->getAliases($app_id, $alias_label, $alias_id);
    print_r($result);
} catch (\onesignal\client\ApiException $e) {
    echo 'Exception when calling DefaultApi->getAliases: ', $e->getMessage(), PHP_EOL;
    echo 'Status Code: ', $e->getCode(), PHP_EOL;
    // getErrorMessages() flattens any error-envelope shape to a string[];
    // the raw body remains on getResponseBody().
    echo 'Error Messages: ', implode(', ', $e->getErrorMessages()), PHP_EOL;
    echo 'Response Body: ', $e->getResponseBody(), PHP_EOL;
} catch (\Exception $e) {
    echo 'Exception when calling DefaultApi->getAliases: ', $e->getMessage(), PHP_EOL;
}

package main

import (
    "context"
    "fmt"
    "os"

    "github.com/OneSignal/onesignal-go-api/v5"
)

func main() {
    appId := "00000000-0000-0000-0000-000000000000" // string | 
    aliasLabel := "external_id" // string | 
    aliasId := "YOUR_USER_EXTERNAL_ID" // string | 

    configuration := onesignal.NewConfiguration()
    apiClient := onesignal.NewAPIClient(configuration)

    restAuth := context.WithValue(context.Background(), onesignal.RestApiKey, "YOUR_REST_API_KEY") // App REST API key required for most endpoints

    resp, r, err := apiClient.DefaultApi.GetAliases(restAuth, appId, aliasLabel, aliasId).Execute()

    if err != nil {
        fmt.Fprintf(os.Stderr, "Error when calling `DefaultApi.GetAliases``: %v\n", err)
        fmt.Fprintf(os.Stderr, "Full HTTP response: %v\n", r)
        if apiErr, ok := err.(*onesignal.GenericOpenAPIError); ok {
            // ErrorMessages() flattens any error-envelope shape to a []string;
            // the raw body remains on Body().
            fmt.Fprintf(os.Stderr, "Error Messages: %v\n", apiErr.ErrorMessages())
            fmt.Fprintf(os.Stderr, "Response Body: %s\n", apiErr.Body())
        }
    }
    // response from `GetAliases`: UserIdentityBody
    fmt.Fprintf(os.Stdout, "Response from `DefaultApi.GetAliases`: %v\n", resp)
}

require 'onesignal'
# setup authorization
OneSignal.configure do |config|
  # Configure Bearer authorization: rest_api_key
  config.rest_api_key = 'YOUR_REST_API_KEY'

end

api_instance = OneSignal::DefaultApi.new
app_id = '00000000-0000-0000-0000-000000000000' # String | 
alias_label = 'external_id' # String | 
alias_id = 'YOUR_USER_EXTERNAL_ID' # String | 

begin
  
  result = api_instance.get_aliases(app_id, alias_label, alias_id)
  p result
rescue OneSignal::ApiError => e
  puts "Error when calling DefaultApi->get_aliases: #{e}"
  puts "Status Code: #{e.code}"
  # `e.error_messages` flattens any error-envelope shape to an Array<String>;
  # the raw body remains on `e.response_body`.
  puts "Error Messages: #{e.error_messages}"
  puts "Response Body: #{e.response_body}"
end

// Import classes:
import com.onesignal.client.ApiClient;
import com.onesignal.client.ApiException;
import com.onesignal.client.Configuration;
import com.onesignal.client.auth.*;
import com.onesignal.client.model.*;
import com.onesignal.client.api.DefaultApi;

public class Example {
  public static void main(String[] args) {
    ApiClient defaultClient = Configuration.getDefaultApiClient();
    defaultClient.setBasePath("https://api.onesignal.com");
    
    // Configure HTTP bearer authorization: rest_api_key
    HttpBearerAuth rest_api_key = (HttpBearerAuth) defaultClient.getAuthentication("rest_api_key");
    rest_api_key.setBearerToken("YOUR_REST_API_KEY");

    DefaultApi apiInstance = new DefaultApi(defaultClient);
    String appId = "00000000-0000-0000-0000-000000000000"; // String | 
    String aliasLabel = "external_id"; // String | 
    String aliasId = "YOUR_USER_EXTERNAL_ID"; // String | 
    try {
      UserIdentityBody result = apiInstance.getAliases(appId, aliasLabel, aliasId);
      System.out.println(result);
    } catch (ApiException e) {
      System.err.println("Exception when calling DefaultApi#getAliases");
      System.err.println("Status code: " + e.getCode());
      // getErrorMessages() flattens any error-envelope shape to a List<String>;
      // the raw body remains on getResponseBody().
      System.err.println("Error messages: " + e.getErrorMessages());
      System.err.println("Reason: " + e.getResponseBody());
      System.err.println("Response headers: " + e.getResponseHeaders());
      e.printStackTrace();
    }
  }
}

using System;
using System.Collections.Generic;
using System.Diagnostics;
using OneSignalApi.Api;
using OneSignalApi.Client;
using OneSignalApi.Model;

namespace Example
{
    public class GetAliasesExample
    {
        public static void Main()
        {
            Configuration config = new Configuration();
            config.BasePath = "https://api.onesignal.com";
            // Configure Bearer token for authorization: rest_api_key
            config.AccessToken = "YOUR_REST_API_KEY";

            var apiInstance = new DefaultApi(config);
            var appId = "00000000-0000-0000-0000-000000000000";  // string | 
            var aliasLabel = "external_id";  // string | 
            var aliasId = "YOUR_USER_EXTERNAL_ID";  // string | 

            try
            {
                UserIdentityBody result = apiInstance.GetAliases(appId, aliasLabel, aliasId);
                Debug.WriteLine(result);
            }
            catch (ApiException  e)
            {
                Debug.Print("Exception when calling DefaultApi.GetAliases: " + e.Message );
                Debug.Print("Status Code: "+ e.ErrorCode);
                // e.ErrorMessages flattens any error-envelope shape to an IReadOnlyList<string>;
                // the raw body remains on e.ErrorContent.
                Debug.Print("Error Messages: " + string.Join(", ", e.ErrorMessages));
                Debug.Print("Response Body: " + e.ErrorContent);
                Debug.Print(e.StackTrace);
            }
        }
    }
}

use onesignal_rust_api::apis::configuration::Configuration;
use onesignal_rust_api::apis::default_api;


#[tokio::main]
async fn main() {
    let mut configuration = Configuration::new();
    configuration.rest_api_key_token = Some("YOUR_REST_API_KEY".to_string());


    // Realistic values are pulled from the spec's `example:` fields where present.
    let app_id: &str = "00000000-0000-0000-0000-000000000000";
    let alias_label: &str = "external_id";
    let alias_id: &str = "YOUR_USER_EXTERNAL_ID";

    match default_api::get_aliases(&configuration, app_id, alias_label, alias_id).await {
        Ok(resp) => println!("{:?}", resp),
        Err(e @ onesignal_rust_api::apis::Error::ResponseError(_)) => {
            // `e.error_messages()` flattens any error-envelope shape to a Vec<String>;
            // the raw response remains on the ResponseError variant.
            eprintln!("get_aliases failed: {:?}", e.error_messages());
        }
        Err(e) => eprintln!("get_aliases failed: {:?}", e),
    }
}

{
  "identity": {
    "onesignal_id": "OneSignal-ID-in-UUID-v4-format",
    "external_id": "the-users-external-id"
  }
}

{
  "errors": [
    {
      "code": "internal error code",
      "title": "example error title"
    }
  ]
}

{
  "errors": [
    {
      "code": "internal error code",
      "title": "example error title"
    }
  ]
}

{
  "errors": [
    {
      "code": "Rate Limit Exceeded",
      "title": "API rate limit exceeded"
    }
  ]
}

{
  "errors": [
    "Service temporarily unavailable"
  ]
}