Build auth API

src/Robware.Auth/Authenticator.cs

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+using System;
+using System.Threading.Tasks;
+
+namespace Robware.Auth {
+	public class Authenticator : IAuthenticator {
+		private readonly IUsers _users;
+		private readonly ICryptographyProvider _crypto;
+
+		public Authenticator(IUsers users, ICryptographyProvider crypto) {
+			_users = users;
+			_crypto = crypto;
+		}
+
+		public async Task<(AuthenticationResult Result, User User)> Authenticate(string username, string password) {
+			try {
+				var user = await _users.GetByEmail(username);
+				return _crypto.Encrypt(password) == user.Password ? (AuthenticationResult.Success, user) : (AuthenticationResult.IncorrectPassword, null);
+			}
+			catch (UserNotFoundException) {
+				return (AuthenticationResult.NotFound, null);
+			}
+		}
+	}
+
+	public enum AuthenticationResult {
+		Unknown,
+		Success,
+		NotFound,
+		IncorrectPassword
+	}
+}

src/Robware.Auth/CryptographyProvider.cs

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+using System.Security.Cryptography;
+using System.Text;
+
+namespace Robware.Auth {
+	public class CryptographyProvider : ICryptographyProvider {
+		public string Encrypt(string input) {
+			using (var sha256 = SHA256.Create()) {
+				var hash = sha256.ComputeHash(Encoding.UTF8.GetBytes(input));
+
+				var builder = new StringBuilder();
+				foreach (var b in hash)
+					builder.Append(b.ToString("x2"));
+				var hashString = builder.ToString();
+
+				return hashString;
+			}
+		}
+	}
+}

src/Robware.Auth/IAuthenticator.cs

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+using System.Threading.Tasks;
+
+namespace Robware.Auth {
+	public interface IAuthenticator {
+		Task<(AuthenticationResult Result, User User)> Authenticate(string username, string password);
+	}
+}

src/Robware.Auth/ICryptographyProvider.cs

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+namespace Robware.Auth {
+	public interface ICryptographyProvider {
+		string Encrypt(string input);
+	}
+}

src/Robware.Auth/IUsers.cs

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+using System.Threading.Tasks;
+
+namespace Robware.Auth {
+	public interface IUsers {
+		Task<User> GetByEmail(string email);
+	}
+}

src/Robware.Auth/Robware.Auth.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
+  </PropertyGroup>
+
+</Project>

src/Robware.Auth/User.cs

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+namespace Robware.Auth {
+	public class User {
+		public string Username { get; protected set; }
+		public string Password { get; protected set; }
+	}
+}

src/Robware.Auth/UserNotFoundException.cs

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+using System;
+
+namespace Robware.Auth {
+	public class UserNotFoundException : Exception {
+		public UserNotFoundException(string username) : base("Could not find user " + username) {
+
+		}
+	}
+}