In C#, when adding multiple service bus clients or administration clients to services, how can we get the correct one back from the service provider?

We have a microservice which needs to be able to send messages, not only to multiple Topics but to Topics which may live on different Azure Service Buses.

In other words, one Topic ("Foo") might need to be accessed by the connection string: Endpoint=sb://;SharedAccessKeyName=RootManageSharedAccessKey;SharedAccessKey=45346346346346346weffv34f43fc32c3d3d23=

and another ("Bar") might need to be accessed by the connection string: Endpoint=sb://;SharedAccessKeyName=RootManageSharedAccessKey;SharedAccessKey=sdvc243r4f4f32c3cd32c23dc2332c2332re=

I'm using the following model to get the connection strings out of the appsettings or Azure portal configuration:

public class MultiServiceBusSettings
    public List<string> ConnectionStrings { get; init; }

    private readonly Regex ConnectionStringPattern = new(@"(?:sb:\/\/)(.*)(?:\/)",
            RegexOptions.Compiled | RegexOptions.ExplicitCapture | RegexOptions.IgnoreCase

    private Dictionary<string, string> _connectionStringsBySubdomain;

    private Dictionary<string, string> ConnectionStringsBySubdomain
            if (_connectionStringsBySubdomain == null)
                _connectionStringsBySubdomain = ConnectionStrings.ToDictionary(x =>
                    Match match = ConnectionStringPattern.Match(x);
                    return match.Success
                        ? match.Groups[1].Value
                        : throw new ArgumentException($"Invalid connection string: {x}");


            return _connectionStringsBySubdomain;

    public string this[string subdomain] =>

And then using the following to add the clients to the solution:

        MultiServiceBusSettings settings = Configure<MultiServiceBusSettings>(services, configuration, configSectionName);
        services.AddAzureClients(builder =>
            foreach (string connectionString in settings.ConnectionStrings)
                _ = builder.AddServiceBusClient(connectionString);
                _ = builder.AddServiceBusAdministrationClient(connectionString);

But now I need to modify the dependencies which will consume either the ServiceBusClient or ServiceBusAdministrationClient.

For example:

public class ServiceBusMessageSender : IMessageSender
    private readonly ServiceBusClient _serviceBusClient;

    public ServiceBusMessageSender(ServiceBusClient serviceBusClient) =>
        _serviceBusClient = serviceBusClient ?? throw new ArgumentNullException(nameof(serviceBusClient));

    // Snipped for brevity

If I don't somehow tell the system which instance of ServiceBusClient to inject, I would expect the methods to at least occasionally fail.

What would be the best (or at least a good) way to fix this?

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