GoogleReCaptchaValidationAttribute.cs

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Net;
using System.Net.Http;
using System.Text.Json;
using System.Text.Json.Serialization;

using Microsoft.Extensions.Configuration;

public class GoogleReCaptchaValidationAttribute : ValidationAttribute
{
    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        if (value == null || string.IsNullOrWhiteSpace(value.ToString()))
        {
            return new ValidationResult(
                "Google reCAPTCHA validation failed. Value is null or empty.",
                new[] { validationContext.MemberName });
        }

        var configuration = (IConfiguration)validationContext.GetService(typeof(IConfiguration));
        if (configuration == null || string.IsNullOrWhiteSpace(configuration["GoogleReCaptcha:Secret"]))
        {
            return new ValidationResult(
                "Google reCAPTCHA validation failed. Secret key not found.",
                new[] { validationContext.MemberName });
        }

        var httpClient = new HttpClient();
        var content = new FormUrlEncodedContent(
            new[]
                {
                    new KeyValuePair<string, string>("secret", configuration["GoogleReCaptcha:Secret"]),
                    new KeyValuePair<string, string>("response", value.ToString()),
                    //// new KeyValuePair<string, string>("remoteip", remoteIp),
                });
        var httpResponse = httpClient.PostAsync($"https://www.google.com/recaptcha/api/siteverify", content)
            .GetAwaiter().GetResult();
        if (httpResponse.StatusCode != HttpStatusCode.OK)
        {
            return new ValidationResult(
                $"Google reCAPTCHA validation failed. Status code: {httpResponse.StatusCode}.",
                new[] { validationContext.MemberName });
        }

        var jsonResponse = httpResponse.Content.ReadAsStringAsync().Result;
        var siteVerifyResponse = JsonSerializer.Deserialize<ReCaptchaSiteVerifyResponse>(jsonResponse);
        return siteVerifyResponse.Success
                   ? ValidationResult.Success
                   : new ValidationResult(
                       "Google reCAPTCHA validation failed.",
                       new[] { validationContext.MemberName });
    }

    public class ReCaptchaSiteVerifyResponse
    {
        [JsonPropertyName("success")]
        public bool Success { get; set; }

        [JsonPropertyName("score")]
        public float Score { get; set; }

        [JsonPropertyName("action")]
        public string Action { get; set; }

        [JsonPropertyName("challenge_ts")]
        public DateTime ChallengeTime { get; set; }

        [JsonPropertyName("hostname")]
        public string Hostname { get; set; }

        [JsonPropertyName("error-codes")]
        public string[] ErrorCodes { get; set; }
    }
}