Core_Be/Helpers/RequestAccessTokenHelper.cs

using Microsoft.IdentityModel.Tokens;
using System.IdentityModel.Tokens.Jwt;
using System.Security.Claims;
using System.Text;

namespace Fitness_core_BE.Helpers
{
    // Mints/validates the short-lived "requestAccessToken" used between mobile-OTP verification
    // and onboarding-request creation. Separate from the RSA-signed AuthHex tokens validated by
    // CustomMiddleware, since this repo only holds the AuthHex *public* key (no local RSA signing key).
    public class RequestAccessTokenHelper
    {
        private readonly string _signingKey;
        private readonly int _expiresInMinutes;

        public RequestAccessTokenHelper(IConfiguration configuration)
        {
            _signingKey = configuration["RequestAccessToken:SigningKey"]
                ?? throw new InvalidOperationException("RequestAccessToken:SigningKey is not configured.");
            _expiresInMinutes = int.TryParse(configuration["RequestAccessToken:ExpiresInMinutes"], out var m) ? m : 15;
        }

        public (string token, int expiresIn) Generate(string mobileNumber)
        {
            var key = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(_signingKey));
            var creds = new SigningCredentials(key, SecurityAlgorithms.HmacSha256);

            var claims = new[]
            {
                new Claim("MobileNumber", mobileNumber),
                new Claim("Purpose", "RequestAccess")
            };

            var expires = DateTime.UtcNow.AddMinutes(_expiresInMinutes);
            var token = new JwtSecurityToken(
                claims: claims,
                expires: expires,
                signingCredentials: creds);

            return (new JwtSecurityTokenHandler().WriteToken(token), _expiresInMinutes * 60);
        }

        public string? ValidateAndGetMobileNumber(string token)
        {
            var key = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(_signingKey));
            var handler = new JwtSecurityTokenHandler();

            try
            {
                var principal = handler.ValidateToken(token, new TokenValidationParameters
                {
                    ValidateIssuer = false,
                    ValidateAudience = false,
                    ValidateLifetime = true,
                    ValidateIssuerSigningKey = true,
                    IssuerSigningKey = key,
                    ClockSkew = TimeSpan.FromMinutes(2)
                }, out _);

                if (principal.FindFirst("Purpose")?.Value != "RequestAccess")
                    return null;

                return principal.FindFirst("MobileNumber")?.Value;
            }
            catch
            {
                return null;
            }
        }
    }
}