SERVERLESS AUTHENTICATION SYSTEM

The goal of this project/repository is to demo how to develop a serverless authentication and authorization service using GoLang and Azure Services. ie. serveless storage and compute.

Prerequisites

• Azure Functions Core Tools, v4
• Go SDK
• Visual Studio Code & Azure Functions extension
• Azure CLI [optional]

Mac or Linux machine, or Windows WSL2 are preferred. All the commands within the sample assumed running in bash.

Create Azure Function Resource

This flow is dev friendly when it comes to quick experiments. For production deployments please consider infrastructure as code and automation via DevOps. In VS Code with Azure Functions extension installed:

• CMD+Shift+P type Azure Functions: Create Function App in Azure... (Advanced) and follow the wizard (further is the example of the steps)
• Select dev subscription
• Enter a globally unique name for the new function app
• Select a runtime stack: Custom Handler
• Select an OS: Linux
• Select a hosting plan: Consumption
• Create a new resource group
• Enter the name of the new resource group
• Create new storage account
• Enter the name of the new storage account
• Create new Application Insights resource
• Enter the name of the new Application Insights resource
• Select a location for new resources (closer to your location)

Don't forget to remove the resource group after experiments to avoid any unpredictable charges

Project structure highlights

• .vscode/ - VSCode settings folder, mostly standard.
• functions/ - everything related to Azure Functions, isolation makes things simpler while no mixing with custom handler related project files
  • Functions folders, containing function.json file
  • .funcignore - functions ignore file with handy ignore options
  • host.json - host configuration file, mostly standard, interesting and important section is customHandler, especially "enableForwardingHttpRequest": true which is not added by default
  • local.settings[.sample].json - contains configuration which is needed for local development and debug, local settings should be excluded from Git to avoid secrets leak
• pkg/ - pkg sub package containing packaged consumed by the application handlers, this involes database interaction, validation, token generation and validation etc.
• Makefile - useful tasks/commands collection for project automation
• README - contains basic project decription and documentation

Local start/debug

• Copy/rename local.settings.sample.json to local.settings.json.

• Provide authentication parameters:

  • MONGODB_CONNECTION_URI

• Start the local server with func start in the functions/ folder

• Navigate to one of the URL endpoints printed in the console

Debugging Go code

For breaking points debugging in VSCode a number of approaches can be used: attaching to process or connecting to server. In most cases, one would prefer restarting Go server without stoping and restarting func start session. Also, it's simpler to place a breakpoint, switch to main.go file, and launch debug. Such a scenario can be covered with:

make debug

The local function app is started without actually starting the Go side-car server, but mimicking the process for functions core utility.

Then, the Go application can be started or restarted as many times as needed, e.g. using go run ./ from the cmd/ folder.

Build and deploy

1. Run build command:

make build

The assumption is that a Linux plan was selected for the function app.

The build creates cmd in the functions/ folder with binary of the Go custom handler.

2. In VSCode,

• CMD+Shift+P type Azure Functions: Deploy to Function App...
• Select subscription
• Select Function App in Azure
• Confirm deployment

Configure environment variables

In the Azure Function app, create and provide the following environment variables:

• MONGODB_CONNECTION_URI

Overriding host's settings

Azure Functions use .Net native approaches dealing with settings. Hierarchical settings can be overriden with environment variables.

E.g., you need cmd.exe locally for windows but a Linux Functions host still needs cmd (without extention) in hosts.json, it can be redefined in local.settings.json with a value:

{
  // ...
  "Values": {
    // ...
    "AzureFunctionsJobHost__customHandler__description__defaultExecutablePath": "bin/server"
  }
}

Adding new function

1. CMD+Shift+P type Azure Functions: Create Function...

2. Select a template for your function, e.g. HTTP trigger

3. Provide a function name. e.g. HttpTrigger1

4. Select authorization level, e.g. Function

A function's folder and bindings definition is created functions/HttpTrigger1/function.json:

{
  "bindings": [
    {
      "authLevel": "function",
      "type": "httpTrigger",
      "direction": "in",
      "name": "req",
      "methods": ["get", "post"]
    },
    {
      "type": "http",
      "direction": "out",
      "name": "res"
    }
  ]
}

5. Run func start in the functions/ folder and follow via http://localhost:7071/api/HttpTrigger1 for just created function's binding

The Echo service handler will response with URL path /api/HttpTrigger1, that's because created function is not processed with specific route Go custom handler yet.

Ctrl+C to stop running functions host.

6. Create handlers/HttpTrigger1.go and paste:

package handlers
import (
	"fmt"
	"net/http"
)
// HTTPTrigger1 handles a function's logic
func (h *Handlers) HTTPTrigger1(w http.ResponseWriter, r *http.Request) {
	name := r.URL.Query().Get("name")
	fmt.Fprintf(w, "Hello, %s!", name)
}

7. Bind a handler with a route in mux.go in API routes section:

http.HandleFunc("/api/HttpTrigger1", h.HTTPTrigger1)

8. Run make start and navigate to http://localhost:7071/api/HttpTrigger1?name=Function

Hello, Function! should be responded back.

Reference

• Azure Functions custom handlers
• Create a Go function in Azure using VSCode
• Functions Custom Handlers (Go)
• Serverless Go in Azure Functions with custom handlers (video)

Author ✒️

• Evans M Opilo - evansopilo

License 🔒

This repository contains a variety of content; some developed by Evans Opilo, and some from third-parties. The third-party content is distributed under the license provided by those parties.

I am providing code and resources in this repository to you under an open source license. Because this is my personal repository, the license you receive to my code and resources is from me and not my employer.

The content developed by Evans Opilo is distributed under the following license:

Text

The text content is released under the CC-BY-NC-ND license. Read more at Creative Commons.

Code

The code in this repository is released under the MIT license, see the LICENSE file for details.