How to get connected clients and client certificate in node-opcua server

I have a node-opcua server setup with 2 clients connected to it with Security Mode set to SignAndEncrypt. Now, I have 2 questions:

1. Is there a way for the server to find out how many clients are connected to it?
2. The server application will like to know the identity of a connected client, is there an API to get the client certificate obtained during OpenSecureChannel?

OPCUA Server can expose such information under the RootFolder.Server.ServerDiagnostics node, and the information you need shall be accessible through OPCUA.

This little node-opcua client program will show you how to do.

note:

• that certain data such as security diagnostics requires a secure connection and a non-anonymous user

client_extract_server_diagnostic.ts

// this script is typescript and can be run this way
// $ npx ts-node client_extract_server_diagnostic.ts

import { 
    AttributeIds,
    OPCUAClient,
    ClientSession, 
    StatusCodes,
    MessageSecurityMode,
    SecurityPolicy,
    UserIdentityInfoUserName,
    UserTokenType   
} from "node-opcua";

// the opcua server to connect to
const endpointUrl = "opc.tcp://localhost:48010";

// the credential 
const userIdentityToken: UserIdentityInfoUserName = {
    password: "secret",
    userName: "root",
    type: UserTokenType.UserName
};

async function extractServerStatistics(session: ClientSession) {

    const nodesToRead = [
        { 
            attributeIds: AttributeIds.Value, nodeId:"Server_ServerDiagnostics_EnabledFlag" 
        },
        { 
            attributeIds: AttributeIds.Value, nodeId:"Server_ServerDiagnostics_ServerDiagnosticsSummary_CurrentSessionCount" //i=2277 
        },
        {
            attributeIds: AttributeIds.Value, nodeId:"Server_ServerDiagnostics_ServerDiagnosticsSummary_CurrentSubscriptionCount" // i=2285 
        },
        {
            attributeIds: AttributeIds.Value, nodeId: "Server_ServerDiagnostics_ServerDiagnosticsSummary_CumulatedSessionCount" // i=2278 
        },
        {
            attributeIds: AttributeIds.Value, nodeId: "Server_ServerDiagnostics_ServerDiagnosticsSummary_CumulatedSubscriptionCount" // i=2278 
        },
        {
            attributeIds: AttributeIds.Value, nodeId: "Server_ServerDiagnostics_SessionsDiagnosticsSummary_SessionSecurityDiagnosticsArray" // i=3708 
        }

    ];
    const dataValues = await session.read(nodesToRead);

    console.log("Diagnostic enabled ?         = ", dataValues[0].value.value);
    console.log("Current Session Count        = ", dataValues[1].value.value);
    console.log("Current Subscription Count   = ", dataValues[2].value.value);
    console.log("Cumulated Session Count      = ", dataValues[3].value.value);
    console.log("Cumulated Subscription Count = ", dataValues[4].value.value);

    // note reading SessionSecurityDiagnotiscArray may requires authenticated session to succeed
    console.log("SessionSecurityDiagnotiscArray       = ");

    if (dataValues[5].statusCode === StatusCodes.Good) {
        const sessionSecurityDiagnosticArray = dataValues[5].value.value;
        // console.log(dataValues[5].value.value.toString());
        for (const sessionSecurityDiagnostic of sessionSecurityDiagnosticArray)  {
            console.log(" session client certificate ", sessionSecurityDiagnostic.clientCertificate.toString("base64"));
            console.log();
        }
    } else {
        console.log(dataValues[5].toString());
    }
}
( async () => {

    try {
        const client = OPCUAClient.create({
            endpoint_must_exist: false,
            securityMode: MessageSecurityMode.SignAndEncrypt,
            securityPolicy: SecurityPolicy.Basic256Sha256,

        });
        client.on("backoff",() => console.log("still trying to connec to ", endpointUrl));

        await client.connect(endpointUrl);

        const session = await client.createSession(userIdentityToken);

        await extractServerStatistics(session);

        await session.close();
        await client.disconnect();
        console.log("done");
    } catch(err) {
        console.log("Err" , err.message);
        process.exit(1);
    }
})();