R3 two-factor sign-in: TOTP with recovery codes, asked for only after a correct password

Completion program R3 (docs/ROADMAP.md, 2026-10-17).

- Services/TwoFactor.cs: TOTP (RFC 6238, 30 s, 6 digits, SHA-1, one step of slack, Otp.NET 1.4.1) and ten recovery
  codes (SHA-256 kept, pulled when used). RootUser.Totp holds the secret, the last step taken (moved only by a
  conditional update, so a code works once even for two sign-ins at the same moment) and the codes' hashes.
- /clientapi/user/totp/setup (the password) answers the secret, its otpauth:// URI and a QR code as an SVG data URI
  (QRCoder 1.8.0); /totp/enable takes the app's first code, shows the recovery codes once and ends every other session
  (this device gets a new one); /totp/disable takes the password and a code. GET /clientapi/user/account says whether
  it is on and how many recovery codes are left.
- Sign-in (/clientapi/user/login, the invitation login, /oauth/login) asks for LoginForm.OneTimeCode with a 428, and
  only once the password was right; the OAuth page has the field. Recovery by email leaves two-factor on.
- PrivaPub admin reset-totp <root>: the way back for a login that lost its authenticator and its codes.
- scenarios/accounts.sh checks it all, with codes computed in Python; the OAuth page with its antiforgery token.

Verified: dotnet build PrivaPub.sln -c Release; the pasture (gts, mailpit): accounts 45/45.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WpVCoDeM1qUTRp4fXQdfof

PrivaPub.ClientModels/LoginForm.cs

@@ -34,5 +34,10 @@ namespace PrivaPub.ClientModels
 		public bool ThemeIsDarkMode { get; set; } = false;
 
 		public string InvitationPassword { get; set; }
+
+		// the authenticator app's code, or one of the recovery codes, for a login with two-factor sign-in; asked for with a
+		// 428 once the password was right
+		[StringLength(32, ErrorMessageResourceName = "MaxLengthString", ErrorMessageResourceType = typeof(ErrorsResource))]
+		public string OneTimeCode { get; set; }
 	}
 }

PrivaPub.ClientModels/User/AccountForms.cs

@@ -49,5 +49,46 @@ namespace PrivaPub.ClientModels.User
 		public bool IsEmailValidated { get; set; } = false;
 		public string PendingEmail { get; set; }//waiting for its code
 		public DateTime CreatedAt { get; set; }
+		public bool TwoFactorEnabled { get; set; } = false;
+		public int RecoveryCodesLeft { get; set; } = 0;
+	}
+
+	// a code from the authenticator app (six digits) or a recovery code
+	public class TotpCodeForm
+	{
+		[Required(ErrorMessageResourceName = "Required", ErrorMessageResourceType = typeof(ErrorsResource)),
+			StringLength(32, MinimumLength = 6, ErrorMessageResourceName = "StringLengthMinMax", ErrorMessageResourceType = typeof(ErrorsResource)),
+			Display(Name = "RecoveryCode", ResourceType = typeof(FieldsNameResource))]
+		public string Code { get; set; }
+	}
+
+	public class TotpDisableForm
+	{
+		[Required(ErrorMessageResourceName = "Required", ErrorMessageResourceType = typeof(ErrorsResource)),
+			DataType(DataType.Password),
+			PasswordPropertyText(true),
+			StringLength(Constants.MaxPasswordLength, ErrorMessageResourceName = "MaxLengthString", ErrorMessageResourceType = typeof(ErrorsResource)),
+			Display(Name = "Password", ResourceType = typeof(FieldsNameResource))]
+		public string Password { get; set; }
+
+		[Required(ErrorMessageResourceName = "Required", ErrorMessageResourceType = typeof(ErrorsResource)),
+			StringLength(32, MinimumLength = 6, ErrorMessageResourceName = "StringLengthMinMax", ErrorMessageResourceType = typeof(ErrorsResource)),
+			Display(Name = "RecoveryCode", ResourceType = typeof(FieldsNameResource))]
+		public string Code { get; set; }
+	}
+
+	// what an authenticator app needs: the secret, as text and as the otpauth:// URI its QR code holds
+	public class ViewTotpSetup
+	{
+		public string Secret { get; set; }
+		public string OtpAuthUri { get; set; }
+		public string QrDataUri { get; set; }//an SVG image, as a data: URI
+	}
+
+	// shown once: the recovery codes, and this device's new session (turning two-factor on ends every other one)
+	public class ViewTotpEnabled
+	{
+		public List<string> RecoveryCodes { get; set; } = [];
+		public JwtUser Session { get; set; }
 	}
 }