MQTTnet v3.0.5 TLS/SSL连接报错：证书类型转换失败求助

问题场景 #

使用MQTTnet v3.0.5版本配置TLS连接时，配置MqttClientOptionsBuilderTlsParameters的Certificates属性出现编译错误：

无法将类型'System.Collections.Generic.List<System.Security.Cryptography.X509Certificates.X509Certificate>'隐式转换为'System.Collections.Generic.IEnumerable<System.Collections.Generic.IEnumerable>'。存在显式转换(是否缺少强制转换?)

错误代码示例：

var caCert = X509Certificate.CreateFromCertFile(@"certificate.crt");
var clientCert = new X509Certificate2(@"certificate.pfx", "12345678");

var tlsOptions = new MqttClientOptionsBuilderTlsParameters
{
     UseTls = true,
     Certificates = new List<X509Certificate>
     {
          caCert, clientCert
     },
     IgnoreCertificateRevocationErrors = true,
     IgnoreCertificateChainErrors = true,
     AllowUntrustedCertificates = true,
     SslProtocol = System.Security.Authentication.SslProtocols.Tls12
};

问题原因 #

MQTTnet v3.0.5版本中，MqttClientOptionsBuilderTlsParameters.Certificates属性的类型为IEnumerable<IEnumerable<byte>>，要求传入证书的字节数组集合，而非直接传入X509Certificate对象列表。

解决方案 #

方案1：升级MQTTnet版本 #

将MQTTnet升级至v3.1.1及以上的v3分支版本，该版本已调整Certificates属性的类型，支持直接传入X509Certificate或X509Certificate2对象列表，原代码可直接正常运行，此方案适用于多数v3分支应用。

方案2：旧版本临时适配（不推荐） #

若无法升级版本，可将证书转换为字节数组集合传入：

var caCert = X509Certificate.CreateFromCertFile(@"certificate.crt");
var clientCert = new X509Certificate2(@"certificate.pfx", "12345678");

var tlsOptions = new MqttClientOptionsBuilderTlsParameters
{
     UseTls = true,
     Certificates = new List<IEnumerable<byte>>
     {
          caCert.Export(X509ContentType.Cert),
          clientCert.Export(X509ContentType.Pfx, "12345678")
     },
     IgnoreCertificateRevocationErrors = true,
     IgnoreCertificateChainErrors = true,
     AllowUntrustedCertificates = true,
     SslProtocol = System.Security.Authentication.SslProtocols.Tls12
};

内容的提问来源于stack exchange，提问作者Trang Phan