Use DI to configure HttpClient.  If you have multiple services then create a factory.  These concepts are covered in official documentation.

https://docs.microsoft.com/en-us/dotnet/api/system.net.http.httpclient?view=net-5.0

https://docs.microsoft.com/en-us/aspnet/core/fundamentals/http-requests?view=aspnetcore-5.0

Tim Cadieux

I tried use a Base Class, but then I went around in circles trying to call HttpContext from static class, etc...I've looked for examples but there is so much noise online re: HttpClient or HttpClient Factory, I don't know where to start.

I feel a base class makes the DI code overly complex.  Use standard DI service patterns and C# generics.   Your service interface will have GET, POST, PUT, DELETE, etc. and perhaps a few method overloads loads.

For example

public interface IApiService
{
    Task<T> GetAsync<T>(string accessToken, string restApi);
}

public async Task<T> GetAsync<T>(string accessToken, string restApi)
{
    _logger.LogDebug($"Api = {restApi}");

    T results = (T)Activator.CreateInstance(typeof(T));

    var client = _httpClientFactory.CreateClient(_apiFactoryName);
    if (!string.IsNullOrEmpty(accessToken))
    {
        client.SetBearerToken(accessToken);
    }
           
    using (Stream s = await client.GetStreamAsync($"{restApi}"))
    {
        using (StreamReader sr = new StreamReader(s))
        {
            using (JsonReader reader = new JsonTextReader(sr))
            {
                JsonSerializer serializer = new JsonSerializer();
                results = serializer.Deserialize<T>(reader);
            }
        }
    }
    return results;
}

Your POST implementation will also have input models.