Add Steam OpenID authentication

2026-07-20 00:30:06 -05:00
parent 18c3d6fc5d
commit cde0e28e44
16 changed files with 564 additions and 29 deletions
@@ -0,0 +1,66 @@
+using System.Text.RegularExpressions;
+
+namespace AuthApi.Services;
+
+public class SteamOpenIdService
+{
+    public const string Endpoint = "https://steamcommunity.com/openid/login";
+    private static readonly Regex ClaimedIdPattern = new(
+        "^https?://steamcommunity\\.com/openid/id/(?<id>[0-9]{17})$",
+        RegexOptions.Compiled | RegexOptions.CultureInvariant);
+    private readonly IHttpClientFactory _httpClients;
+
+    public SteamOpenIdService(IHttpClientFactory httpClients) => _httpClients = httpClients;
+
+    public static string BuildAuthenticationUrl(string realm, string returnUrl)
+    {
+        var parameters = new Dictionary<string, string>
+        {
+            ["openid.ns"] = "http://specs.openid.net/auth/2.0",
+            ["openid.mode"] = "checkid_setup",
+            ["openid.return_to"] = returnUrl,
+            ["openid.realm"] = realm,
+            ["openid.identity"] = "http://specs.openid.net/auth/2.0/identifier_select",
+            ["openid.claimed_id"] = "http://specs.openid.net/auth/2.0/identifier_select"
+        };
+        return Endpoint + "?" + string.Join("&", parameters.Select(pair =>
+            $"{Uri.EscapeDataString(pair.Key)}={Uri.EscapeDataString(pair.Value)}"));
+    }
+
+    public async Task<string?> VerifyCallbackAsync(IQueryCollection query, string expectedReturnUrl, CancellationToken cancellationToken)
+    {
+        if (!string.Equals(query["openid.mode"], "id_res", StringComparison.Ordinal) ||
+            !string.Equals(query["openid.op_endpoint"].ToString().TrimEnd('/'), Endpoint.TrimEnd('/'), StringComparison.OrdinalIgnoreCase) ||
+            !string.Equals(query["openid.return_to"], expectedReturnUrl, StringComparison.Ordinal))
+            return null;
+
+        var claimedId = query["openid.claimed_id"].ToString();
+        if (!string.Equals(claimedId, query["openid.identity"], StringComparison.Ordinal))
+            return null;
+        var match = ClaimedIdPattern.Match(claimedId);
+        if (!match.Success)
+            return null;
+
+        var fields = query
+            .Where(pair => pair.Key.StartsWith("openid.", StringComparison.Ordinal))
+            .ToDictionary(pair => pair.Key, pair => pair.Value.ToString());
+        fields["openid.mode"] = "check_authentication";
+        var client = _httpClients.CreateClient(nameof(SteamOpenIdService));
+        client.Timeout = TimeSpan.FromSeconds(15);
+        using var response = await client.PostAsync(Endpoint, new FormUrlEncodedContent(fields), cancellationToken);
+        if (!response.IsSuccessStatusCode)
+            return null;
+        var validation = await response.Content.ReadAsStringAsync(cancellationToken);
+        return IsValidAuthenticationResponse(validation) ? match.Groups["id"].Value : null;
+    }
+
+    internal static bool IsValidAuthenticationResponse(string response) =>
+        response.Split('\n', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries)
+            .Any(line => string.Equals(line, "is_valid:true", StringComparison.Ordinal));
+
+    internal static string? ExtractSteamId(string claimedId)
+    {
+        var match = ClaimedIdPattern.Match(claimedId);
+        return match.Success ? match.Groups["id"].Value : null;
+    }
+}