diff --git a/src/Api/Controllers/SsoCookieVendorController.cs b/src/Api/Controllers/SsoCookieVendorController.cs
new file mode 100644
index 0000000000..f160b14d73
--- /dev/null
+++ b/src/Api/Controllers/SsoCookieVendorController.cs
@@ -0,0 +1,117 @@
+using Bit.Core.Settings;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+
+namespace Bit.Api.Controllers;
+
+/// <summary>
+/// Provides an endpoint to read an SSO cookie and redirect to a custom URI
+/// scheme. The load balancer must be configured such that requests to this
+/// endpoint do not have the auth cookie stripped.
+/// </summary>
+[Route("sso-cookie-vendor")]
+public class SsoCookieVendorController(IGlobalSettings globalSettings) : Controller
+{
+    private readonly IGlobalSettings _globalSettings = globalSettings;
+    private const int _maxShardCount = 20;
+    private const int _maxUriLength = 8192;
+
+    /// <summary>
+    /// Reads SSO cookie (shards supported) and redirects to the bitwarden://
+    /// URI with cookie value(s).
+    /// </summary>
+    /// <returns>
+    /// 302 redirect on success, 404 if no cookies found, 400 if URI too long,
+    /// 500 if misconfigured
+    /// </returns>
+    [HttpGet]
+    [AllowAnonymous]
+    public IActionResult Get()
+    {
+        var bootstrap = _globalSettings.Communication?.Bootstrap;
+        if (string.IsNullOrEmpty(bootstrap) || bootstrap != "ssoCookieVendor")
+        {
+            return NotFound();
+        }
+
+        var cookieName = _globalSettings.Communication?.SsoCookieVendor?.CookieName;
+        if (string.IsNullOrWhiteSpace(cookieName))
+        {
+            return StatusCode(500, "SSO cookie vendor is not properly configured");
+        }
+
+        var uri = string.Empty;
+        if (TryGetCookie(cookieName, out var cookie))
+        {
+            uri = BuildRedirectUri(cookie);
+        }
+        else if (TryGetShardedCookie(cookieName, out var shardedCookie))
+        {
+            uri = BuildRedirectUri(shardedCookie);
+        }
+
+        if (uri == string.Empty)
+        {
+            return NotFound("No SSO cookies found");
+        }
+
+        if (uri.Length > _maxUriLength)
+        {
+            return BadRequest();
+        }
+
+        return Redirect(uri);
+    }
+
+    private bool TryGetCookie(string cookieName, out Dictionary<string, string> cookie)
+    {
+        cookie = [];
+
+        if (Request.Cookies.TryGetValue(cookieName, out var value) && !string.IsNullOrEmpty(value))
+        {
+            cookie[cookieName] = value;
+            return true;
+        }
+
+        return false;
+    }
+
+    private bool TryGetShardedCookie(string cookieName, out Dictionary<string, string> cookies)
+    {
+        var shardedCookies = new Dictionary<string, string>();
+
+        for (var i = 0; i < _maxShardCount; i++)
+        {
+            var shardName = $"{cookieName}-{i}";
+            if (Request.Cookies.TryGetValue(shardName, out var value) && !string.IsNullOrEmpty(value))
+            {
+                shardedCookies[shardName] = value;
+            }
+            else
+            {
+                // Stop at first missing shard to maintain order integrity
+                break;
+            }
+        }
+
+        cookies = shardedCookies;
+        return shardedCookies.Count > 0;
+    }
+
+    private static string BuildRedirectUri(Dictionary<string, string> cookies)
+    {
+        var queryParams = new List<string>();
+
+        foreach (var kvp in cookies)
+        {
+            var encodedValue = Uri.EscapeDataString(kvp.Value);
+            queryParams.Add($"{kvp.Key}={encodedValue}");
+        }
+
+        // Add a sentinel value so clients can detect a truncated URI, in the
+        // event a user agent decides the URI is too long.
+        queryParams.Add("d=1");
+
+        return $"bitwarden://sso_cookie_vendor?{string.Join("&", queryParams)}";
+    }
+}
diff --git a/test/Api.Test/Controllers/SsoCookieVendorControllerTests.cs b/test/Api.Test/Controllers/SsoCookieVendorControllerTests.cs
new file mode 100644
index 0000000000..1e954e68ff
--- /dev/null
+++ b/test/Api.Test/Controllers/SsoCookieVendorControllerTests.cs
@@ -0,0 +1,362 @@
+#nullable enable
+
+using Bit.Api.Controllers;
+using Bit.Core.Settings;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Mvc;
+using NSubstitute;
+using Xunit;
+
+namespace Bit.Api.Test.Controllers;
+
+public class SsoCookieVendorControllerTests : IDisposable
+{
+    private readonly SsoCookieVendorController _sut;
+    private readonly GlobalSettings _globalSettings;
+
+    public SsoCookieVendorControllerTests()
+    {
+        _globalSettings = new GlobalSettings
+        {
+            Communication = new GlobalSettings.CommunicationSettings
+            {
+                Bootstrap = "ssoCookieVendor",
+                SsoCookieVendor = new GlobalSettings.SsoCookieVendorSettings
+                {
+                    CookieName = "test-cookie"
+                }
+            }
+        };
+        _sut = new SsoCookieVendorController(_globalSettings);
+    }
+
+    public void Dispose()
+    {
+        _sut?.Dispose();
+    }
+
+    private void MockHttpContextWithCookies(Dictionary<string, string> cookies)
+    {
+        var httpContext = new DefaultHttpContext();
+        var cookieCollection = Substitute.For<IRequestCookieCollection>();
+
+        // Mock the TryGetValue method
+        cookieCollection.TryGetValue(Arg.Any<string>(), out Arg.Any<string?>())
+            .Returns(callInfo =>
+            {
+                var key = callInfo.ArgAt<string>(0);
+                if (cookies.TryGetValue(key, out var value))
+                {
+                    callInfo[1] = value;
+                    return true;
+                }
+                callInfo[1] = null;
+                return false;
+            });
+
+        // Mock the indexer if needed
+        cookieCollection[Arg.Any<string>()].Returns(callInfo =>
+        {
+            var key = callInfo.ArgAt<string>(0);
+            return cookies.TryGetValue(key, out var value) ? value : null;
+        });
+
+        httpContext.Request.Cookies = cookieCollection;
+        _sut.ControllerContext = new ControllerContext { HttpContext = httpContext };
+    }
+
+    [Theory]
+    [InlineData(null)]
+    [InlineData("")]
+    [InlineData("none")]
+    public void Get_WhenBootstrapNotConfigured_Returns404(string? bootstrap)
+    {
+        // Arrange
+#nullable disable
+        _globalSettings.Communication.Bootstrap = bootstrap;
+#nullable restore
+        MockHttpContextWithCookies([]);
+
+        // Act
+        var result = _sut.Get();
+
+        // Assert
+        Assert.IsType<NotFoundResult>(result);
+    }
+
+    [Fact]
+    public void Get_WhenCookieNameNotConfigured_Returns500()
+    {
+        // Arrange
+        _globalSettings.Communication.SsoCookieVendor.CookieName = string.Empty;
+        MockHttpContextWithCookies([]);
+
+        // Act
+        var result = _sut.Get();
+
+        // Assert
+        var statusCodeResult = Assert.IsType<ObjectResult>(result);
+        Assert.Equal(500, statusCodeResult.StatusCode);
+    }
+
+    [Fact]
+    public void Get_WhenCookieNameIsEmpty_Returns500()
+    {
+        // Arrange
+        _globalSettings.Communication.SsoCookieVendor.CookieName = "";
+        MockHttpContextWithCookies([]);
+
+        // Act
+        var result = _sut.Get();
+
+        // Assert
+        var statusCodeResult = Assert.IsType<ObjectResult>(result);
+        Assert.Equal(500, statusCodeResult.StatusCode);
+    }
+
+    [Fact]
+    public void Get_WhenSingleCookieExists_ReturnsRedirectWithCorrectUri()
+    {
+        // Arrange
+        var cookies = new Dictionary<string, string>
+        {
+            { "test-cookie", "my-token-value-123" }
+        };
+        MockHttpContextWithCookies(cookies);
+
+        // Act
+        var result = _sut.Get();
+
+        // Assert
+        var redirectResult = Assert.IsType<RedirectResult>(result);
+        Assert.Equal("bitwarden://sso_cookie_vendor?test-cookie=my-token-value-123&d=1", redirectResult.Url);
+    }
+
+    [Fact]
+    public void Get_WhenSingleCookieHasSpecialCharacters_EncodesCorrectly()
+    {
+        // Arrange
+        var cookies = new Dictionary<string, string>
+        {
+            { "test-cookie", "value with spaces & special=chars!" }
+        };
+        MockHttpContextWithCookies(cookies);
+
+        // Act
+        var result = _sut.Get();
+
+        // Assert
+        var redirectResult = Assert.IsType<RedirectResult>(result);
+        Assert.Contains("value%20with%20spaces", redirectResult.Url);
+        Assert.Contains("%26", redirectResult.Url); // & encoded
+        Assert.Contains("%3D", redirectResult.Url); // = encoded
+        Assert.Contains("%21", redirectResult.Url); // ! encoded
+    }
+
+    [Fact]
+    public void Get_WhenShardedCookiesExist_ReturnsRedirectWithShardedUri()
+    {
+        // Arrange
+        var cookies = new Dictionary<string, string>
+        {
+            { "test-cookie-0", "part1" },
+            { "test-cookie-1", "part2" },
+            { "test-cookie-2", "part3" }
+        };
+        MockHttpContextWithCookies(cookies);
+
+        // Act
+        var result = _sut.Get();
+
+        // Assert
+        var redirectResult = Assert.IsType<RedirectResult>(result);
+        Assert.StartsWith("bitwarden://sso_cookie_vendor?", redirectResult.Url);
+        Assert.Contains("test-cookie-0=part1", redirectResult.Url);
+        Assert.Contains("test-cookie-1=part2", redirectResult.Url);
+        Assert.Contains("test-cookie-2=part3", redirectResult.Url);
+        Assert.EndsWith("d=1", redirectResult.Url);
+    }
+
+    [Fact]
+    public void Get_WhenShardedCookiesWithGap_StopsAtFirstGap()
+    {
+        // Arrange
+        var cookies = new Dictionary<string, string>
+        {
+            { "test-cookie-0", "part0" },
+            { "test-cookie-1", "part1" },
+            // Missing test-cookie-2
+            { "test-cookie-3", "part3" },
+            { "test-cookie-4", "part4" }
+        };
+        MockHttpContextWithCookies(cookies);
+
+        // Act
+        var result = _sut.Get();
+
+        // Assert
+        var redirectResult = Assert.IsType<RedirectResult>(result);
+        Assert.Contains("test-cookie-0=part0", redirectResult.Url);
+        Assert.Contains("test-cookie-1=part1", redirectResult.Url);
+        Assert.DoesNotContain("test-cookie-3", redirectResult.Url);
+        Assert.DoesNotContain("test-cookie-4", redirectResult.Url);
+        Assert.EndsWith("d=1", redirectResult.Url);
+    }
+
+    [Fact]
+    public void Get_WhenOnlyGappedShardsExist_Returns404()
+    {
+        // Arrange - only test-cookie-2 exists, not test-cookie-0 or test-cookie-1
+        var cookies = new Dictionary<string, string>
+        {
+            { "test-cookie-2", "part2" },
+            { "test-cookie-3", "part3" }
+        };
+        MockHttpContextWithCookies(cookies);
+
+        // Act
+        var result = _sut.Get();
+
+        // Assert
+        Assert.IsType<NotFoundObjectResult>(result);
+    }
+
+    [Fact]
+    public void Get_WhenNoCookiesFound_Returns404()
+    {
+        // Arrange
+        MockHttpContextWithCookies([]);
+
+        // Act
+        var result = _sut.Get();
+
+        // Assert
+        Assert.IsType<NotFoundObjectResult>(result);
+    }
+
+    [Fact]
+    public void Get_WhenUnrelatedCookiesExist_Returns404()
+    {
+        // Arrange
+        var cookies = new Dictionary<string, string>
+        {
+            { "other-cookie", "value" },
+            { "another-cookie", "value2" }
+        };
+        MockHttpContextWithCookies(cookies);
+
+        // Act
+        var result = _sut.Get();
+
+        // Assert
+        Assert.IsType<NotFoundObjectResult>(result);
+    }
+
+    [Fact]
+    public void Get_WhenUriExceedsMaxLength_Returns400()
+    {
+        // Arrange - create a very long cookie value that will exceed 8192 characters
+        // URI format: "bitwarden://sso_cookie_vendor?test-cookie={value}"
+        // Base URI length is about 43 characters, so we need value > 8149
+        var longValue = new string('a', 8200);
+        var cookies = new Dictionary<string, string>
+        {
+            { "test-cookie", longValue }
+        };
+        MockHttpContextWithCookies(cookies);
+
+        // Act
+        var result = _sut.Get();
+
+        // Assert
+        Assert.IsType<BadRequestResult>(result);
+    }
+
+    [Fact]
+    public void Get_WhenSingleCookiePreferredOverSharded_ReturnsSingleCookie()
+    {
+        // Arrange - both single and sharded cookies exist
+        var cookies = new Dictionary<string, string>
+        {
+            { "test-cookie", "single-value" },
+            { "test-cookie-0", "shard0" },
+            { "test-cookie-1", "shard1" }
+        };
+        MockHttpContextWithCookies(cookies);
+
+        // Act
+        var result = _sut.Get();
+
+        // Assert
+        var redirectResult = Assert.IsType<RedirectResult>(result);
+        Assert.Equal("bitwarden://sso_cookie_vendor?test-cookie=single-value&d=1", redirectResult.Url);
+    }
+
+    [Fact]
+    public void Get_WhenEmptyCookieValue_TreatsAsNotFound()
+    {
+        // Arrange
+        var cookies = new Dictionary<string, string>
+        {
+            { "test-cookie", "" }
+        };
+        MockHttpContextWithCookies(cookies);
+
+        // Act
+        var result = _sut.Get();
+
+        // Assert
+        Assert.IsType<NotFoundObjectResult>(result);
+    }
+
+    [Fact]
+    public void Get_WhenShardedCookiesHaveMaxCount_ProcessesAllShards()
+    {
+        // Arrange - create 20 sharded cookies (MaxShardCount)
+        var cookies = new Dictionary<string, string>();
+        for (var i = 0; i < 20; i++)
+        {
+            cookies[$"test-cookie-{i}"] = $"part{i}";
+        }
+        MockHttpContextWithCookies(cookies);
+
+        // Act
+        var result = _sut.Get();
+
+        // Assert
+        var redirectResult = Assert.IsType<RedirectResult>(result);
+        for (var i = 0; i < 20; i++)
+        {
+            Assert.Contains($"test-cookie-{i}=part{i}", redirectResult.Url);
+        }
+        Assert.EndsWith("d=1", redirectResult.Url);
+    }
+
+    [Fact]
+    public void Get_WhenShardedCookiesExceedMaxCount_OnlyProcessesFirst20()
+    {
+        // Arrange - create 25 sharded cookies (more than MaxShardCount of 20)
+        var cookies = new Dictionary<string, string>();
+        for (var i = 0; i < 25; i++)
+        {
+            cookies[$"test-cookie-{i}"] = $"part{i}";
+        }
+        MockHttpContextWithCookies(cookies);
+
+        // Act
+        var result = _sut.Get();
+
+        // Assert
+        var redirectResult = Assert.IsType<RedirectResult>(result);
+        // Should contain first 20
+        for (var i = 0; i < 20; i++)
+        {
+            Assert.Contains($"test-cookie-{i}=part{i}", redirectResult.Url);
+        }
+        // Should NOT contain 21-25
+        for (var i = 20; i < 25; i++)
+        {
+            Assert.DoesNotContain($"test-cookie-{i}=part{i}", redirectResult.Url);
+        }
+    }
+}