Configure service with user-related parameters in .NET Core dependency injection

Here are my observations:

• Startup.ServiceProvider.GetService<ILogger<GoogleCloudService>>();: As you might know Inversion of Control are usually achieved either via Dependency Injection or via Service Locator. The later one should be avoided if possible. So, please prefer Dependency Injection:

public class GoogleCloudService
{
    private readonly ILogger<GoogleCloudService> logger;

    public GoogleCloudService(string key, ILogger<GoogleCloudService> logger)
    {
        Key = key;
        this.logger = logger;
    }

• public string Key { get; set; }: Do you really need to expose this as public? Do you really need to allow external modification?

  • If no then private readonly string key would be sufficient or if you stick to property then private string Key { get; init; }

• using (var client = new HttpClient()): You don't need to create and dispose an HttpClient for each and every request. Please prefer a static HttpClient per domain or use HttpClientFactory if you can.

• Convert.ToBase64String(imageBytes): I would suggest to perform some sort of preliminary check to make sure that imageBytes are not null and contains some data

• var jsonSettings = new JsonSerializerOptions(); This could be declared as static because this is not changing from request to request

• await response.Content.ReadFromJsonAsync<dynamic>: Try to avoid deserializing data into dynamic. Please create a concrete class, which could be used as the contract between your client and the service provider. dynamic can hide a lot of problems

• responseJson.responses[0] is not null: This might cause OutOfRangeException if the responses is defined but empty. Please check the collection's length as well prior accessing a member directly

• throw new HttpRequestException();: According to my understanding you will never reach this code. The else block is also unnecessary:

if (responseJson is not null 
    && responseJson.responses is not null 
    && responseJson.responses.Length > 0
    && responseJson.responses[0] is not null 
    && responseJson.responses[0].fullTextAnnotation is not null)
{
    return responseJson.responses[0].fullTextAnnotation.text;
}

return null;

• ex.Data.Add("Request", await response.RequestMessage.ToRawAsync()); Capturing the whole request-response might be expensive if their body are too lengthy. It might make sense to truncate them. Please bear in mind that you already have values variable which contains the request body. Please also bear in mind that you are not capture headers, which might contain valuable information
• catch(Exception ex): You can get rid of the outer try-catch if you perform preliminary checks

if(imageBytes == null || (imagesBytes != null && imagesBytes.Length < 1))
   return ...

var values = new ...
var response = await client.PostAsJsonAsync(url, values);

try
{
    response.EnsureSuccessStatusCode();
    ...
    {
        return responseJson.responses[0].fullTextAnnotation.text;
    }
    return null;
}
catch (Exception ex)
{
    ex.Data.Add("Request", await response.RequestMessage.ToRawAsync());
    ex.Data.Add("Response", await response.ToRawAsync());

    logger.LogError(ex, "Возникла ошибка при отправке запроса в Google Cloud.");
}

UPDATE: Reflect to comment

You can create a Factory method which is responsible for creating GoogleCloudService instances. You can take advantage ILoggerFactory (Reference) to avoid Service Locator.

public class GoogleCloudServiceFactory: ICloudServiceFactory
{
   private readonly ILoggerFactory loggerFactory;
   public GoogleCloudServiceFactory(ILoggerFactory loggerFactory)
   {
      this.loggerFactory = loggerFactory;
   }

   public ICloudService Create(string key)
   {
      return new GoogleCloudService(key, loggerFactory);
   }
}

Usage

foreach (var entityDB in entities)             
{                 
    ICloudService gService = serviceFactory.Create(entityDB.GoogleApiKey);                 
    string text = await gService.ImageTextRecognizeAsync(entityDB.ImageBytes);             
}