Media.JoshHeaps.Net/Api/SsoApi.cs

@@ -0,0 +1,175 @@
+using System.IdentityModel.Tokens.Jwt;
+using System.Security.Claims;
+using System.Security.Cryptography;
+using System.Text;
+using Media.JoshHeaps.Net.Services;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.IdentityModel.Tokens;
+using Npgsql;
+
+namespace Media.JoshHeaps.Net.Api;
+
+[ApiController]
+[Route("sso")]
+public class SsoApi(DbExecutor db, IConfiguration config, ILogger<SsoApi> logger) : ControllerBase
+{
+    [HttpPost("token")]
+    public async Task<IActionResult> Exchange([FromBody] SsoTokenRequest request)
+    {
+        if (request == null || string.IsNullOrWhiteSpace(request.ClientId) || string.IsNullOrWhiteSpace(request.Code))
+        {
+            return BadRequest(new { error = "client_id and code are required" });
+        }
+
+        if (!Request.Headers.TryGetValue("X-Client-Secret", out var providedSecret) || string.IsNullOrWhiteSpace(providedSecret))
+        {
+            return Unauthorized(new { error = "missing client credentials" });
+        }
+
+        var client = SsoClientRegistry.Find(config, request.ClientId);
+        if (client == null || !BCrypt.Net.BCrypt.Verify(providedSecret!, client.ClientSecretHash))
+        {
+            logger.LogWarning("SSO token exchange failed: bad client credentials for {ClientId}", request.ClientId);
+            return Unauthorized(new { error = "invalid client credentials" });
+        }
+
+        var codeHash = HashCode(request.Code);
+        var row = await ConsumeCodeAsync(codeHash);
+        if (row == null)
+        {
+            return BadRequest(new { error = "invalid, expired, or already-used code" });
+        }
+
+        if (!string.Equals(row.Value.ClientId, request.ClientId, StringComparison.Ordinal))
+        {
+            return BadRequest(new { error = "code was issued for a different client" });
+        }
+
+        if (!client.AllowsRedirectUri(row.Value.RedirectUri))
+        {
+            return BadRequest(new { error = "redirect_uri mismatch" });
+        }
+
+        var user = await LoadUserAsync(row.Value.UserId);
+        if (user == null)
+        {
+            return BadRequest(new { error = "user no longer exists" });
+        }
+
+        var jwt = IssueToken(user, request.ClientId);
+        return Ok(new SsoTokenResponse
+        {
+            AccessToken = jwt,
+            TokenType = "Bearer",
+            ExpiresIn = 300
+        });
+    }
+
+    private async Task<(long UserId, string ClientId, string RedirectUri)?> ConsumeCodeAsync(string codeHash)
+    {
+        var connectionString = config["connectionString"]!;
+        await using var conn = new NpgsqlConnection(connectionString);
+        await conn.OpenAsync();
+        await using var tx = await conn.BeginTransactionAsync();
+
+        long userId;
+        string clientId;
+        string redirectUri;
+
+        await using (var select = new NpgsqlCommand(
+            @"SELECT user_id, client_id, redirect_uri
+              FROM app.sso_authorization_codes
+              WHERE code_hash = @h
+                AND consumed_at IS NULL
+                AND expires_at > NOW()
+              FOR UPDATE", conn, tx))
+        {
+            select.Parameters.AddWithValue("@h", codeHash);
+            await using var reader = await select.ExecuteReaderAsync();
+            if (!await reader.ReadAsync()) return null;
+            userId = reader.GetInt64(0);
+            clientId = reader.GetString(1);
+            redirectUri = reader.GetString(2);
+        }
+
+        await using (var update = new NpgsqlCommand(
+            "UPDATE app.sso_authorization_codes SET consumed_at = NOW() WHERE code_hash = @h",
+            conn, tx))
+        {
+            update.Parameters.AddWithValue("@h", codeHash);
+            await update.ExecuteNonQueryAsync();
+        }
+
+        await tx.CommitAsync();
+        return (userId, clientId, redirectUri);
+    }
+
+    private async Task<SsoUser?> LoadUserAsync(long userId)
+    {
+        return await db.ExecuteReaderAsync(
+            "SELECT id, email, username, email_verified FROM app.users WHERE id = @userId AND is_active = true",
+            reader => new SsoUser
+            {
+                Id = reader.GetInt64(0),
+                Email = reader.GetString(1),
+                Username = reader.GetString(2),
+                EmailVerified = reader.GetBoolean(3)
+            },
+            new { userId });
+    }
+
+    private string IssueToken(SsoUser user, string audience)
+    {
+        var jwtKey = config["Jwt:Key"] ?? throw new InvalidOperationException("JWT Key not configured");
+        var jwtIssuer = config["Jwt:Issuer"] ?? throw new InvalidOperationException("JWT Issuer not configured");
+
+        var securityKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(jwtKey));
+        var credentials = new SigningCredentials(securityKey, SecurityAlgorithms.HmacSha256);
+
+        var claims = new[]
+        {
+            new Claim(JwtRegisteredClaimNames.Sub, user.Id.ToString()),
+            new Claim(ClaimTypes.NameIdentifier, user.Id.ToString()),
+            new Claim(ClaimTypes.Email, user.Email),
+            new Claim(ClaimTypes.Name, user.Username),
+            new Claim("EmailVerified", user.EmailVerified.ToString()),
+            new Claim(JwtRegisteredClaimNames.Jti, Guid.NewGuid().ToString("N"))
+        };
+
+        var token = new JwtSecurityToken(
+            issuer: jwtIssuer,
+            audience: audience,
+            claims: claims,
+            expires: DateTime.UtcNow.AddMinutes(5),
+            signingCredentials: credentials);
+
+        return new JwtSecurityTokenHandler().WriteToken(token);
+    }
+
+    private static string HashCode(string code)
+    {
+        var bytes = SHA256.HashData(Encoding.UTF8.GetBytes(code));
+        return Convert.ToHexString(bytes).ToLowerInvariant();
+    }
+}
+
+public sealed class SsoTokenRequest
+{
+    public string ClientId { get; set; } = string.Empty;
+    public string Code { get; set; } = string.Empty;
+}
+
+public sealed class SsoTokenResponse
+{
+    public string AccessToken { get; set; } = string.Empty;
+    public string TokenType { get; set; } = "Bearer";
+    public int ExpiresIn { get; set; }
+}
+
+internal sealed class SsoUser
+{
+    public long Id { get; set; }
+    public string Email { get; set; } = string.Empty;
+    public string Username { get; set; } = string.Empty;
+    public bool EmailVerified { get; set; }
+}

Media.JoshHeaps.Net/Database/030_sso_authorization_codes.sql

@@ -0,0 +1,15 @@
+-- SSO authorization codes for the OAuth2 authorization-code flow.
+-- The raw code is never stored; we persist the SHA-256 hash only.
+-- Codes are single-use and short-lived (see Sso:CodeLifetimeSeconds in config).
+
+CREATE TABLE IF NOT EXISTS app.sso_authorization_codes (
+    code_hash       TEXT PRIMARY KEY,
+    client_id       TEXT NOT NULL,
+    user_id         BIGINT NOT NULL REFERENCES app.users(id) ON DELETE CASCADE,
+    redirect_uri    TEXT NOT NULL,
+    expires_at      TIMESTAMPTZ NOT NULL,
+    consumed_at     TIMESTAMPTZ,
+    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_sso_codes_expires ON app.sso_authorization_codes(expires_at);

Media.JoshHeaps.Net/Pages/Login.cshtml

@@ -43,6 +43,10 @@
 
         <form id="loginForm" method="post">
             @Html.AntiForgeryToken()
+            @if (!string.IsNullOrEmpty(Model.ReturnUrl))
+            {
+                <input type="hidden" name="ReturnUrl" value="@Model.ReturnUrl" />
+            }
             <div class="form-group">
                 <label for="email" class="form-label">Email or Username</label>
                 <input type="text" class="form-control" id="email" name="email"

Media.JoshHeaps.Net/Pages/Login.cshtml.cs

@@ -16,6 +16,9 @@ public class LoginModel(AuthService authService) : PageModel
     [BindProperty]
     public bool RememberMe { get; set; }
 
+    [BindProperty(SupportsGet = true)]
+    public string? ReturnUrl { get; set; }
+
     public string? ErrorMessage { get; set; }
     public string? SuccessMessage { get; set; }
     public string? WarningMessage { get; set; }
@@ -26,7 +29,7 @@ public class LoginModel(AuthService authService) : PageModel
         var userId = HttpContext.Session.GetString("UserId");
         if (!string.IsNullOrEmpty(userId))
         {
-            Response.Redirect("/Landing");
+            Response.Redirect(SafeReturnUrl() ?? "/Landing");
             return;
         }
 
@@ -90,6 +93,9 @@ public class LoginModel(AuthService authService) : PageModel
             Response.Cookies.Append("RememberMe", userInfo.Id.ToString(), cookieOptions);
         }
 
-        return Redirect("/Landing");
+        return Redirect(SafeReturnUrl() ?? "/Landing");
     }
+
+    private string? SafeReturnUrl() =>
+        !string.IsNullOrWhiteSpace(ReturnUrl) && Url.IsLocalUrl(ReturnUrl) ? ReturnUrl : null;
 }

Media.JoshHeaps.Net/Pages/Sso/Authorize.cshtml

@@ -0,0 +1,5 @@
+@page "/sso/authorize"
+@model Media.JoshHeaps.Net.Pages.Sso.AuthorizeModel
+@{
+    Layout = null;
+}

Media.JoshHeaps.Net/Pages/Sso/Authorize.cshtml.cs

@@ -0,0 +1,59 @@
+using System.Security.Cryptography;
+using System.Text;
+using Media.JoshHeaps.Net.Services;
+using Microsoft.AspNetCore.Mvc;
+
+namespace Media.JoshHeaps.Net.Pages.Sso;
+
+public class AuthorizeModel(DbExecutor db, IConfiguration config, ILogger<AuthorizeModel> logger) : AuthenticatedPageModel
+{
+    public async Task<IActionResult> OnGetAsync(
+        [FromQuery(Name = "client_id")] string? clientId,
+        [FromQuery(Name = "redirect_uri")] string? redirectUri,
+        [FromQuery] string? state)
+    {
+        if (string.IsNullOrWhiteSpace(clientId) || string.IsNullOrWhiteSpace(redirectUri) || string.IsNullOrWhiteSpace(state))
+        {
+            return BadRequest("client_id, redirect_uri, and state are required");
+        }
+
+        var client = SsoClientRegistry.Find(config, clientId);
+        if (client == null) return BadRequest("unknown client_id");
+        if (!client.AllowsRedirectUri(redirectUri)) return BadRequest("redirect_uri is not registered for this client");
+
+        if (!IsAuthenticated())
+        {
+            var original = $"/sso/authorize?client_id={Uri.EscapeDataString(clientId)}&redirect_uri={Uri.EscapeDataString(redirectUri)}&state={Uri.EscapeDataString(state)}";
+            return Redirect($"/Login?ReturnUrl={Uri.EscapeDataString(original)}");
+        }
+
+        LoadUserSession();
+
+        var code = GenerateCode();
+        var codeHash = HashCode(code);
+        var lifetime = int.TryParse(config["Sso:CodeLifetimeSeconds"], out var s) ? s : 60;
+        var expiresAt = DateTimeOffset.UtcNow.AddSeconds(lifetime);
+
+        await db.ExecuteNonQueryAsync(
+            @"INSERT INTO app.sso_authorization_codes (code_hash, client_id, user_id, redirect_uri, expires_at)
+              VALUES (@codeHash, @clientId, @userId, @redirectUri, @expiresAt)",
+            new { codeHash, clientId, userId = UserId, redirectUri, expiresAt });
+
+        logger.LogInformation("SSO code issued for user {UserId} to client {ClientId}", UserId, clientId);
+
+        var separator = redirectUri.Contains('?') ? '&' : '?';
+        return Redirect($"{redirectUri}{separator}code={Uri.EscapeDataString(code)}&state={Uri.EscapeDataString(state)}");
+    }
+
+    private static string GenerateCode()
+    {
+        var bytes = RandomNumberGenerator.GetBytes(32);
+        return Convert.ToBase64String(bytes).Replace("+", "-").Replace("/", "_").TrimEnd('=');
+    }
+
+    private static string HashCode(string code)
+    {
+        var bytes = SHA256.HashData(Encoding.UTF8.GetBytes(code));
+        return Convert.ToHexString(bytes).ToLowerInvariant();
+    }
+}

Media.JoshHeaps.Net/Services/SsoClientRegistry.cs

@@ -0,0 +1,21 @@
+namespace Media.JoshHeaps.Net.Services;
+
+public sealed class SsoClientConfig
+{
+    public string ClientId { get; set; } = string.Empty;
+    public string ClientSecretHash { get; set; } = string.Empty;
+    public List<string> RedirectUris { get; set; } = [];
+    public string Name { get; set; } = string.Empty;
+
+    public bool AllowsRedirectUri(string uri) =>
+        RedirectUris.Any(r => string.Equals(r, uri, StringComparison.Ordinal));
+}
+
+public static class SsoClientRegistry
+{
+    public static SsoClientConfig? Find(IConfiguration config, string clientId)
+    {
+        var clients = config.GetSection("Sso:Clients").Get<List<SsoClientConfig>>() ?? [];
+        return clients.FirstOrDefault(c => string.Equals(c.ClientId, clientId, StringComparison.Ordinal));
+    }
+}

Media.JoshHeaps.Net/appsettings.json

@@ -24,6 +24,17 @@
     "InvalidateUrl": "https://joshheaps.net/api/blog/invalidate",
     "InvalidateKey": "CHANGE_ME"
   },
+  "Sso": {
+    "CodeLifetimeSeconds": 60,
+    "Clients": [
+      {
+        "ClientId": "ai",
+        "ClientSecretHash": "SET_VIA_USER_SECRETS",
+        "RedirectUris": [ "https://ai.joshheaps.net/auth/callback" ],
+        "Name": "AI JoshHeaps"
+      }
+    ]
+  },
   "FileUpload": {
     "MaxFileSizeMB": 10,
     "AllowedImageTypes": ["image/jpeg", "image/png", "image/gif", "image/webp"],