网页通过C#webapi访问服务器opcua获得数据，给出代码

好的，以下是一个简单的示例代码，用于通过C# Web API访问服务器OPC UA并获取数据：

using Opc.Ua;
using Opc.Ua.Client;
using System.Threading.Tasks;
using System.Web.Http;

public class OpcUaController : ApiController
{
    [HttpGet]
    public async Task<string> GetOpcUaData()
    {
        // 初始化OPC UA客户端
        var endpointUrl = "opc.tcp://localhost:4840"; // OPC UA服务器的URL和端口号
        var applicationConfiguration = new ApplicationConfiguration()
        {
            ApplicationName = "OPC UA Client",
            ApplicationType = ApplicationType.Client,
            SecurityConfiguration = new SecurityConfiguration
            {
                ApplicationCertificate = new CertificateIdentifier { StoreType = @"Windows", StorePath = @"CurrentUser\My", SubjectName = "OPC UA Client" },
                TrustedPeerCertificates = new CertificateTrustList { StoreType = @"Windows", StorePath = @"CurrentUser\TrustedPeople", },
                TrustedIssuerCertificates = new CertificateTrustList { StoreType = @"Windows", StorePath = @"CurrentUser\TrustedPublisher", },
                RejectedCertificateStore = new CertificateTrustList { StoreType = @"Windows", StorePath = @"CurrentUser\Disallowed", },
                AutoAcceptUntrustedCertificates = true,
                AddAppCertToTrustedStore = true,
            },
            TransportConfigurations = new TransportConfigurationCollection(),
        };
        var endpointConfiguration = EndpointConfiguration.Create(applicationConfiguration);
        var selectedEndpoint = CoreClientUtils.SelectEndpoint(endpointUrl, true, 5000);
        var endpoint = new ConfiguredEndpoint(null, selectedEndpoint, endpointConfiguration);
        var session = await Session.Create(applicationConfiguration, endpoint, true, "OPC UA Client", 60000, new UserIdentity(new AnonymousIdentityToken()), null);

        // 浏览服务器名称空间并查找节点
        var browseDescription = new BrowseDescription
        {
            NodeId = new NodeId(ObjectIds.ObjectsFolder),
            BrowseDirection = BrowseDirection.Forward,
            ReferenceTypeId = ReferenceTypeIds.HierarchicalReferences,
            IncludeSubtypes = true,
            NodeClassMask = 0u,
            ResultMask = (uint)BrowseResultMask.All,
        };
        var browseResult = await session.BrowseAsync(browseDescription);
        var objectsFolder = browseResult.References.Find(r => r.DisplayName.Text == "Objects");
        var dataFolder = await session.ReadNodeAsync(new NodeId(objectsFolder.NodeId.ToString() + "/Data"));
        var dataNode = await session.ReadNodeAsync(new NodeId(dataFolder.Value.ToString() + "/MyDataNode"));

        // 读取节点的值
        var value = await session.ReadValueAsync(dataNode.NodeId);

        // 处理读取的数据并返回
        return value.Value.ToString();
    }
}

请注意，此代码仅用于演示目的，实际实现可能需要更多的错误处理和安全性措施。