前言
上一篇已经介绍了identity的注册，登录，获取jwt token，本篇来完成refresh token。
开始
开始之前先说明一下为什么需要refresh token。
虽然jwt token有很多优点，但是它的缺点也是非常明显。由于jwt无状态的特性，所以jwt一旦颁发，基本上就不可控了，在过期时间内一直有效。有些场景下我们是希望能控制token失效的，比如用户的重要数据被修改时（密码，角色，权限，等等），我们希望用户重新获取token，甚至重新登录。
那么refresh token就可以很好的弥补jwt的缺陷。虽然refresh token也无法直接控制jwt失效，但是在refresh token机制下，我们可以把token的有效期设置的短一些，比如30分钟，而refresh token的有效期可以很长；因为refresh token会持久化到数据库中，它是完全可控的。
很多人纠结的jwt滑动刷新，无感刷新，在refresh token机制下，都不是问题。
生成refresh_token
改造一下上一篇的代码，首先refresh token需要持久化到数据库中，定义实体：
public class RefreshToken
{[Key]public int Id { get; set; }[Required][StringLength(128)]public string JwtId { get; set; }[Required][StringLength(256)]public string Token { get; set; }/// <summary>/// 是否使用，一个RefreshToken只能使用一次/// </summary>[Required]public bool Used { get; set; }/// <summary>/// 是否失效。修改用户重要信息时可将此字段更新为true，使用户重新登录/// </summary>[Required]public bool Invalidated { get; set; }[Required]public DateTime CreationTime { get; set; }[Required]public DateTime ExpiryTime { get; set; }[Required]public int UserId { get; set; }[Required][ForeignKey(nameof(UserId))]public AppUser User { get; set; }
}加入到DbContext：
public class AppDbContext : IdentityDbContext<AppUser, IdentityRole<int>, int>
{public DbSet<RefreshToken> RefreshTokens { get; set; }public AppDbContext(DbContextOptions<AppDbContext> options): base(options){}// 省略......
}ef迁移：
dotnet ef migrations add AppDbContext_Added_RefreshTokendotnet ef database update登录注册返回token时，也要把RefreshToken和ExpiresIn有效时间一起返回：
public class TokenResult
{public bool Success => Errors == null || !Errors.Any();public IEnumerable<string> Errors { get; set; }public string AccessToken { get; set; }public string TokenType { get; set; }public int ExpiresIn { get; set; } // addpublic string RefreshToken { get; set; } // add
}public class TokenResponse
{[JsonPropertyName("access_token")] public string AccessToken { get; set; }[JsonPropertyName("token_type")] public string TokenType { get; set; }[JsonPropertyName("expires_in")]public int ExpiresIn { get; set; } // add[JsonPropertyName("refresh_token")]public string RefreshToken { get; set; } // add
}修改UserService创建token方法：
private async Task<TokenResult> GenerateJwtToken(AppUser user)
{var key = Encoding.ASCII.GetBytes(_jwtSettings.SecurityKey);var tokenDescriptor = new SecurityTokenDescriptor{Subject = new ClaimsIdentity(new[]{new Claim(JwtRegisteredClaimNames.Jti, Guid.NewGuid().ToString("N")),new Claim(JwtRegisteredClaimNames.Sub, user.Id.ToString())}),IssuedAt = DateTime.UtcNow,NotBefore = DateTime.UtcNow,Expires = DateTime.UtcNow.Add(_jwtSettings.ExpiresIn),SigningCredentials = new SigningCredentials(new SymmetricSecurityKey(key),SecurityAlgorithms.HmacSha256Signature)};var jwtTokenHandler = new JwtSecurityTokenHandler();var securityToken = jwtTokenHandler.CreateToken(tokenDescriptor);var token = jwtTokenHandler.WriteToken(securityToken);var refreshToken = new RefreshToken(){JwtId = securityToken.Id,UserId = user.Id,CreationTime = DateTime.UtcNow,ExpiryTime = DateTime.UtcNow.AddMonths(6),Token = GenerateRandomNumber()};await _appDbContext.RefreshTokens.AddAsync(refreshToken);await _appDbContext.SaveChangesAsync();return new TokenResult(){AccessToken = token,TokenType = "Bearer",RefreshToken = refreshToken.Token,ExpiresIn = (int)_jwtSettings.ExpiresIn.TotalSeconds,};
}private string GenerateRandomNumber(int len = 32)
{var randomNumber = new byte[len];using var rng = RandomNumberGenerator.Create();rng.GetBytes(randomNumber);return Convert.ToBase64String(randomNumber);
}登录测试，已经返回了refresh_token：
使用refresh_token获取token
// RefreshToken 请求参数
public class RefreshTokenRequest
{[JsonPropertyName("access_token")]public string AccessToken { get; set; }[JsonPropertyName("refresh_token")]public string RefreshToken { get; set; }
}public interface IUserService
{// 省略......Task<TokenResult> RefreshTokenAsync(string token, string refreshToken); // add
}RefreshTokenAsync实现：
public async Task<TokenResult> RefreshTokenAsync(string token, string refreshToken)
{var claimsPrincipal = GetClaimsPrincipalByToken(token);if (claimsPrincipal == null){// 无效的token...return new TokenResult(){Errors = new[] { "1: Invalid request!" },};}var expiryDateUnix =long.Parse(claimsPrincipal.Claims.Single(x => x.Type == JwtRegisteredClaimNames.Exp).Value);var expiryDateTimeUtc = UnixTimeStampToDateTime(expiryDateUnix);if (expiryDateTimeUtc > DateTime.UtcNow){// token未过期...return new TokenResult(){Errors = new[] { "2: Invalid request!" },};}var jti = claimsPrincipal.Claims.Single(x => x.Type == JwtRegisteredClaimNames.Jti).Value;var storedRefreshToken =await _appDbContext.RefreshTokens.SingleOrDefaultAsync(x => x.Token == refreshToken);if (storedRefreshToken == null){// 无效的refresh_token...return new TokenResult(){Errors = new[] { "3: Invalid request!" },};}if (storedRefreshToken.ExpiryTime < DateTime.UtcNow){// refresh_token已过期...return new TokenResult(){Errors = new[] { "4: Invalid request!" },};}if (storedRefreshToken.Invalidated){// refresh_token已失效...return new TokenResult(){Errors = new[] { "5: Invalid request!" },};}if (storedRefreshToken.Used){// refresh_token已使用...return new TokenResult(){Errors = new[] { "6: Invalid request!" },};}if (storedRefreshToken.JwtId != jti){// refresh_token与此token不匹配...return new TokenResult(){Errors = new[] { "7: Invalid request!" },};}storedRefreshToken.Used = true;//_userDbContext.RefreshTokens.Update(storedRefreshToken);await _appDbContext.SaveChangesAsync();var dbUser = await _userManager.FindByIdAsync(storedRefreshToken.UserId.ToString());return await GenerateJwtToken(dbUser);
}解析token，注意这里的tokenValidationParameters，这个参数和Startup中设置的tokenValidationParameters唯一的区别是ValidateLifetime = false，不验证过期时间。
private ClaimsPrincipal GetClaimsPrincipalByToken(string token)
{try{var tokenValidationParameters = new TokenValidationParameters{ValidateIssuer = false,ValidateAudience = false,ValidateIssuerSigningKey = true,IssuerSigningKey = new SymmetricSecurityKey(Encoding.ASCII.GetBytes(_jwtSettings.SecurityKey)),ClockSkew = TimeSpan.Zero,ValidateLifetime = false // 不验证过期时间！！！};var jwtTokenHandler = new JwtSecurityTokenHandler();var claimsPrincipal =jwtTokenHandler.ValidateToken(token, tokenValidationParameters, out var validatedToken);var validatedSecurityAlgorithm = validatedToken is JwtSecurityToken jwtSecurityToken&& jwtSecurityToken.Header.Alg.Equals(SecurityAlgorithms.HmacSha256,StringComparison.InvariantCultureIgnoreCase);return validatedSecurityAlgorithm ? claimsPrincipal : null;}catch{return null;}
}最后是UserController：
[HttpPost("RefreshToken")]
public async Task<IActionResult> RefreshToken(RefreshTokenRequest request)
{var result = await _userService.RefreshTokenAsync(request.AccessToken, request.RefreshToken);if (!result.Success){return Unauthorized(new FailedResponse(){Errors = result.Errors});}return Ok(new TokenResponse{AccessToken = result.AccessToken,TokenType = result.TokenType,ExpiresIn = result.ExpiresIn,RefreshToken = result.RefreshToken});
}测试token未过期时刷新token：
正常刷新token：
refresh_token使用一次后，不可以再次使用：
其他情况可以自行测试。。。
最后
总结一下，上面的代码看似很多，其实完成的功能非常简单；就是在用户获取token时，后台生成一个与之对应的refresh token一并返回，同时将refresh token保存到数据库中；refresh token的存在就是为了当token过期时，能免登录刷新一次token。（refresh token只能使用一次，用户重要数据比如密码修改时，可以将refresh token置为失效，使用户重新登录）。代码已上传至 [blogs/asp.net core identity + jwt/code at main · xiajingren/blogs (github.com)](https://github.com/xiajingren/blogs/tree/main/asp.net core identity %2B jwt/code "blogs/asp.net core identity + jwt/code at main · xiajingren/blogs (github.com)")
参考：
ASP.NET Core 简介 Identity | Microsoft Docs[1]
Mohamad Lawand - DEV Community[2]
参考资料
[1]
ASP.NET Core 简介 Identity | Microsoft Docs: https://docs.microsoft.com/zh-cn/aspnet/core/security/authentication/identity?view=aspnetcore-5.0&tabs=visual-studio
[2]Mohamad Lawand - DEV Community: https://dev.to/moe23/comments
