About

This repository contains a sample project used as a basis for a take-home coding test. It is intended for candidates applying for .NET software development role at Humanforce.

Scenario

This Web API project implements a basic online repository for image files. Images can be uploaded, resized and converted, and retrieved from the API.

Instructions

Start by cloning this code repository and ensure that you can build and run the application locally. Use the Postman application to test the API. Import the /Postman/PostmanCollection.json file to get started quickly.

Below you'll find a list of tasks with instructions and approximate time estimates. Choose 1 or 2 of these tasks to complete, or as many as you feel you can get done within approximately 4 hours. Choose the most challenging task(s) that you feel you're able to confidently complete according to your own knowledge and experience.

A single fully-implemented task (with unit tests) is better regarded than multiple incomplete tasks. You'll find an existing project in the solution called UnitTests where you can add unit tests to validate the new functionality that you create.

Feel free to make any changes you like to the existing code or project structure, nothing is set in stone.

Submitting your work

When you're finished please submit your code by sending us a URL to a fork of this repo, or by zipping a clean copy of your local working directory (code files only, no binaries) and sending it to your recruitment contact.

If you have any issues or questions don't hesitate to reach out.

Good luck!

Tasks to choose from

Task 1 - Add KeepAspectRatio parameter

Add a new parameter to the existing /api/image/upload endpoint named KeepAspectRatio. Make changes to the code to implement this parameter as follows:

• If KeepAspectRatio is true the resized image should maintain its original aspect ratio after being resized.
• If TargetWidth is a positive non-zero number then TargetHeight should be ignored, and the new height is determined automatically.
• If TargetWidth is invalid (zero or negative) then the TargetHeight parameter should be used to determine the new width automatically.
• If both TargetWidth and TargetHeight are invalid then the API should return a Bad Reqest.

Time estimate: 1-2 hours

Task 2 - Add Info endpoint

Add a new API endpoint called Info to the ImageController (GET /api/image/info)

The new endpoint should behave as follows:

• Lookup an image from the database by its ID.
• Return a 404 if the image ID is not valid.
• For valid images, return a JSON object containing some information about the image:
  • Original filename
  • Format
  • DateTime created (in UTC)
  • Width
  • Height
  • Stored size in bytes

Time estimate: 1-2 hours

Task 3 - Prevent saving duplicate images

Add a check in the /api/image/upload to prevent the exact same image being saved twice.

• If an image is uploaded that is already in the database then the endpoint should return the ID of the pre-existing image. Include a new boolean field in the response called AlreadyExists to indicate that the duplicate was detected.
• The check for equality should be done based on the image data after resizing and converting. The API should NOT reject the same image if the TargetWidth, TargetHeight or TargetFormat parameters are different to what was uploaded previously.

There are many ways this requirement can be implemented, choose any approach you like. HINT: Consider adding a field to the Images database table to store a hash.

Time estimate: 2-3 hours

Task 4 - Add encryption at rest

Implement encryption at rest in the database to protect the image data.

• Encryption should be added to the Data field of the Images table, other fields may remain unencrypted.
• Use the AES symmetric encryption algorithm with a 256 bit key.
• Store the key material in the appSettings.json file.
• Encryption should be transparent to the callers of the API. I.e. data should be automatically encrypted when imported via the /upload endpoint, and decrypted on the fly when downloaded from the /get endpoint.

Time estimate: 3-4 hours

Task 5 - Add authentication

Add authentication to the /api/image/upload endpoint using a JWT.

• The JWT audience and expiry should be validated.
• Add a new column to the Images database table to hold the username of the person who uploaded the image. Return this data in the /info endpoint (if you have implemented it).
• Choose one of the following two approaches:
  • Integrate with an existing identity provider of your choice (e.g. Okta, Auth0, Microsoft, AWS Cognito, etc.), OR
  • Use self-signed JWTs, storing the public key (or HMAC secret) in the appSettings.json file. Plug your private key or HMAC secret into the Postman application to generate the tokens.

Time estimate: 3-4 hours