public class AccessManageModel
{
    private CosXml cosXml; //Set the service user as a data member
    // Initialize COS service instance
    private void InitCosXml()
    {
        string region = Environment.GetEnvironmentVariable("COS_REGION");
        CosXmlConfig config = new CosXmlConfig.Builder()
            .SetRegion(region) // Set default region. For abbreviations of COS regions, see https://www.tencentcloud.com/document/product/436/6224?from_cn_redirect=1
            .Build();
        string secretId = Environment.GetEnvironmentVariable("SECRET_ID"); // Cloud API key SecretId, see https://console.tencentcloud.com/cam/capi to obtain API key
        string secretKey = Environment.GetEnvironmentVariable("SECRET_KEY"); // cloud API key SecretKey, obtain API key see https://console.tencentcloud.com/cam/capi
        long durationSecond = 600; //Request signature valid duration for each request, in seconds
        QCloudCredentialProvider qCloudCredentialProvider = new DefaultQCloudCredentialProvider(secretId, secretKey, durationSecond);
        this.cosXml = new CosXmlServer(config, qCloudCredentialProvider);
    }
}

public void PutBucketPolicy()
{
    string bucket = "examplebucket-1250000000";
    PutBucketPolicyRequest request = new PutBucketPolicyRequest(bucket);
    string policy = @"{
           ""Statement"": [
               {
                   ""Action"": [
                       ""name/cos:PutBucketPolicy"",
                       ""name/cos:GetBucketPolicy"",
                       ""name/cos:DeleteBucketPolicy""
                   ],
                   ""Effect"": ""Allow"",
                   ""Principal"": {
                       ""qcs"": [
                           ""qcs::cam::uin/100000000001:uin/100000000002""
                       ]
                   },
                   ""Resource"": [
                       ""qcs::cos:ap-guangzhou:uid/1250000000:examplebucket-1250000000/*""
                   ]
               }
           ],
           ""Version"": ""2.0""
      }";
    request.SetBucketPolicy(policy);
    PutBucketPolicyResult result = cosXml.PutBucketPolicy(request);
    Console.WriteLine(result.GetResultInfo());
}

public void GetBucketPolicy()
{
    string bucket = "examplebucket-1250000000";
    GetBucketPolicyRequest  request = new GetBucketPolicyRequest(bucket);
    GetBucketPolicyResult result = cosXml.GetBucketPolicy(request);
    Console.WriteLine(result.Data); //Return Data, in json format
    Console.WriteLine(result.GetResultInfo());
}

public void DeleteBucketPolicy()
{  
    string bucket = "examplebucket-1250000000";
    DeleteBucketPolicyRequest  request = new DeleteBucketPolicyRequest(bucket);
    DeleteBucketPolicyResult result = cosXml.DeleteBucketPolicy(request);
    Console.WriteLine(result.GetResultInfo());
}