问题描述

在APIM中配置对传入的Token进行预验证，确保传入后端被保护的API的Authorization信息正确有效，可以使用validate-jwt策略。validate-jwt 策略强制要求从指定 HTTP 标头或指定查询参数提取的 JSON Web 令牌 (JWT) 必须存在且有效。validate-jwt 策略支持 HS256 和 RS256 签名算法。

对于 HS256，必须在策略中以 base64 编码形式提供内联方式的密钥。
对于 RS256，密钥可以通过 Open ID 配置终结点来提供，或者通过提供包含公钥或公钥的模数指数对的已上传证书的 ID 来提供。

在最开始使用HS256签名算法的Token时，在validate-jwt策略中配置 issuer-signing-keys就能成功验证JWT，但是当使用RS256签名算法适合，这样就不行。会抛出 'System.NotSupportedException: IDX10634: Unable to create the SignatureProvider.\nAlgorithm: 'RS256', SecurityKey: 'Microsoft.IdentityModel.Tokens.SymmetricSecurityKey... 错误。

HS256配置

<validate-jwt header-name="Authorization" failed-validation-httpcode="401" failed-validation-error-message="Unvalid authorization" require-expiration-time="true" require-signed-tokens="true">
            <issuer-signing-keys>
                <key>在HS256算法中使用的密钥，进行base64编码后的值</key>
            </issuer-signing-keys>
            <audiences>
                <audience>在生成JWT Token时设置的aud值</audience>
            </audiences>
   </validate-jwt>

RS256配置（附带错误消息）

<validate-jwt header-name="Authorization" failed-validation-httpcode="401" failed-validation-error-message="Unvalid authorization" require-expiration-time="true" require-signed-tokens="true">
            <issuer-signing-keys>
            <key><RS256 公钥内容通过base64编码后的值></key>
            </issuer-signing-keys>
            <audiences>
                <audience>在生成JWT Token时设置的aud值</audience>
            </audiences>
</validate-jwt>

在进行验证时错误消息（文末附录中包含如何在APIM门户中通过Test功能检测策略的执行结果及错误）

validate-jwt (-0.132 ms)
    {
"message": "JWT Validation Failed: IDX10503: Signature validation failed. 
Keys tried: 'Microsoft.IdentityModel.Tokens.SymmetricSecurityKey, KeyId: '', InternalId: 'HuvkEY3HBhujvk2qeDfgPFD2iYc-GYrnlDX6Yd1LsYQ'. ,
 KeyId: \r\n'.\nExceptions caught:\n 'System.NotSupportedException: IDX10634: Unable to create the SignatureProvider.\nAlgorithm: 'RS256',
SecurityKey: 'Microsoft.IdentityModel.Tokens.SymmetricSecurityKey, KeyId: '', 
InternalId: 'HuvkEY3HBhujvk2qeDfgPFD2iYc-GYrnlDX6Yd1LsYQ'.'\n is not supported. 
The list of supported algorithms is available here: https://aka.ms/IdentityModel/supported-algorithms\r\n   
at Microsoft.IdentityModel.Tokens.CryptoProviderFactory.CreateSignatureProvider(SecurityKey key, String algorithm, Boolean willCreateSignatures, Boolean cacheProvider)\r\n   
at Microsoft.IdentityModel.Tokens.CryptoProviderFactory.CreateForVerifying(SecurityKey key, String algorithm, Boolean cacheProvider)\r\n   
at System.IdentityModel.Tokens.Jwt.JwtSecurityTokenHandler.ValidateSignature(Byte[] encodedBytes, Byte[] signature, SecurityKey key, String algorithm, SecurityToken securityToken, TokenValidationParameters validationParameters)\r\n   
at System.IdentityModel.Tokens.Jwt.JwtSecurityTokenHandler.ValidateSignature(String token, 
TokenValidationParameters validationParameters)\r\n'.
\ntoken: '{\"typ\":\"jwt\",\"alg\":\"RS256\"}.{\"aud\":\"xxxxx.azure-api.cn\",\"user_id\":123456,\"username\":\"lutpython\",\"exp\":1631786725}'.."
}

那么，如何来解决RS256 JWT的验证问题呢？

解决方案

正如APIM官网中特别提醒的一句话“对于 RS256，密钥可以通过 Open ID 配置终结点来提供，或者通过提供包含公钥或公钥的模数指数对的已上传证书的 ID 来提供 (英文原文：For RS256 the key may be provided either via an Open ID configuration endpoint, or by providing the ID of an uploaded certificate that contains the public key or modulus-exponent pair of the public key.)” ，所以APIM 中的validate-jwt是不支持使用直接配置公钥（Public Key）。目前的方案有两种：

1) 使用openid configuration， OpenID Configuration中包含了公钥的内容，是有提供Token的权限服务器管理提供（如 Azure AD中就自动包含OpenID Configuration Endpoint). 注：这部分的详细介绍可以参考官网：https://docs.azure.cn/zh-cn/api-management/api-management-access-restriction-policies#azure-active-directory-token-validation

2) 把有证书机构（CA)颁发的包含公钥（Publick Key）的 .pfx证书上传到APIM中，然后配置 key certificate-id="<上传在APIM证书中的ID值>"

<validate-jwt header-name="Authorization" failed-validation-httpcode="401" failed-validation-error-message="Unvalid authorization" require-expiration-time="true" require-signed-tokens="true">
            <issuer-signing-keys>
                <key certificate-id="<上传在APIM证书中的ID值>" />
            </issuer-signing-keys>
            <audiences>
                <audience>在生成JWT Token时设置的aud值</audience>
            </audiences>
        </validate-jwt>

方案步骤

可以使用以下的步骤来验证RS256 JWT：

1）使用 openssl 指令创建证书（Local.pfx)

openssl.exe req -x509 -nodes -sha256 -days 3650 -subj "/CN=Local" -newkey rsa:2048 -keyout Local.key -out Local.crt

openssl.exe pkcs12 -export -in Local.crt -inkey Local.key -CSP "Microsoft Enhanced RSA and AES Cryptographic Provider" -out Local.pfx

openssl.exe 下载地址：https://slproweb.com/products/Win32OpenSSL.html, 使用时需要 cd到 openssl.exe所在的bin目录中

2）上传 Local.pfx 文件到APIM，并自定义证书ID，如：apim-rs256-01

3）在APIM的策略中（API级，单个操作级别，或者一组API[产品]，或者全部的APIs）。validate-jwt 内容如下：

<policies>
    <inbound>
        <base />
        <validate-jwt header-name="Authorization" failed-validation-httpcode="401" failed-validation-error-message="401 unauthorized">
            <issuer-signing-keys>
                <key certificate-id="apim-rs256-01" />
            </issuer-signing-keys>
        </validate-jwt>
    </inbound>
    <backend>
        <base />
    </backend>
    <outbound>
        <base />
    </outbound>
    <on-error>
        <base />
    </on-error>
</policies>

4) 使用以下的C#代码生成 Token

using Microsoft.IdentityModel.Tokens;
using System;
using System.Collections.Generic;
using System.IdentityModel.Tokens.Jwt;
using System.Linq;
using System.Security.Claims;
using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleAppjwt
{
    class Program
    {
        static void Main(string[] args)
        {            // Token Generation
            var CLIENT_ID = "Local";
            var ISSUER_GUID = "b0123cec-86bb-4eb2-8704-dcf7cb2cc279";
            var filePath = @"C:\Users\xxxx\source\repos\ConsoleAppjwt\ConsoleAppjwt\Cert\Local.pfx";
            var x509Certificate2 = new X509Certificate2(filePath, "123456789");
            var signingCredentials = new X509SigningCredentials(x509Certificate2, SecurityAlgorithms.RsaSha256Signature); //, SecurityAlgorithms.Sha256Digest
            var tokenHandler = new JwtSecurityTokenHandler();
            var originalIssuer = $"{CLIENT_ID}";
            var issuer = originalIssuer;
            DateTime utcNow = DateTime.UtcNow;
            DateTime expired = utcNow + TimeSpan.FromHours(1);
            var claims = new List<Claim> {
         new Claim("aud", "https://login.microsoftonline.com/{YOUR_TENENT_ID}/oauth2/token", ClaimValueTypes.String, issuer, originalIssuer),
         new Claim("exp", "1460534173", ClaimValueTypes.DateTime, issuer, originalIssuer),
         new Claim("jti", $"{ISSUER_GUID}", ClaimValueTypes.String, issuer, originalIssuer),
         new Claim("nbf", "1460533573", ClaimValueTypes.String, issuer, originalIssuer),
         new Claim("sub", $"{CLIENT_ID}", ClaimValueTypes.String, issuer, originalIssuer)
     };
            ClaimsIdentity subject = new ClaimsIdentity(claims: claims);
            var tokenDescriptor = new SecurityTokenDescriptor
            {
                Subject = subject,
                Issuer = issuer,
                Expires = expired,
                SigningCredentials = signingCredentials,
            };
            JwtSecurityToken jwtToken = tokenHandler.CreateToken(tokenDescriptor) as JwtSecurityToken;
            jwtToken.Header.Remove("typ");
            var token = tokenHandler.WriteToken(jwtToken);
            Console.WriteLine(token);
            //Start to Verify Token
            Console.WriteLine("Start to Verify Token");
            ValidationToken(token);
            Console.ReadLine();
        }
        static void ValidationToken(string token)
        {
            try
            {
                JwtSecurityTokenHandler jwtHandler = new JwtSecurityTokenHandler();
                var filePath = @"C:\Users\xxxx\source\repos\ConsoleAppjwt\ConsoleAppjwt\Cert\Local.pfx";
                TokenValidationParameters tvParameter = new TokenValidationParameters
                {
                    ValidateIssuerSigningKey = true,
                    IssuerSigningKey = new X509SecurityKey(new X509Certificate2(filePath, "123456789")),
                    ValidateIssuer = false,
                    ValidateAudience = false,
                    // set clockskew to zero so tokens expire exactly at token expiration time (instead of 5 minutes later)
                    ClockSkew = TimeSpan.Zero
                };
                SecurityToken stoken;
                jwtHandler.ValidateToken(token, tvParameter, out stoken);
                Console.WriteLine(stoken);
                Console.WriteLine("Validate Token Success");
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex);
            }
        }
    }
}