OWIN Invalid URI: The Uri String is too long - sql-server

Question

I have an MVC application hosted on a server (IIS) which points to 3 SQL databases. This has been running without issues for months.
I've just had to change the connectionstrings for all 3 SQL databases to point to new databases.
Now when I try to log in I get the following error..
The connection strings are using Windows Authentication and this account is set in the AppPool. I've also manually tried to connect to each database instance with the account and this works fine. I'm beginning to think the change is SQL connections is just a red herring.
In terms of the error message, I totally understand what the error is Im just not sure why its being thrown. The only thing I can think of is I'm in some kind of redirect loop which is appending the URL.
It definitely feels like an IIS issue but I can't put my finger on it.
Has anyone come across this before with OWIN or can advise on debugging steps that might diagnose the issue?
Startup.cs
public partial class Startup
{
private static bool IsAjaxRequest(IOwinRequest request)
{
IReadableStringCollection query = request.Query;
if ((query != null) && (query["X-Requested-With"] == "XMLHttpRequest"))
{
return true;
}
IHeaderDictionary headers = request.Headers;
return ((headers != null) && (headers["X-Requested-With"] == "XMLHttpRequest"));
}
public void ConfigureAuth(IAppBuilder app)
{
// Configure the db context, user manager and role manager to use a single instance per request
app.CreatePerOwinContext(ParentDbContext.Create);
app.CreatePerOwinContext<ApplicationUserManager>(ApplicationUserManager.Create);
app.CreatePerOwinContext<ApplicationRoleManager>(ApplicationRoleManager.Create);
app.CreatePerOwinContext<ApplicationSignInManager>(ApplicationSignInManager.Create);
app.CreatePerOwinContext(PrincipalManager.Create);
// Enable the application to use a cookie to store information for the signed in user
// and to use a cookie to temporarily store information about a user logging in with a third party login provider
// Configure the sign in cookie
app.UseCookieAuthentication(new CookieAuthenticationOptions
{
AuthenticationType = DefaultAuthenticationTypes.ApplicationCookie,
LoginPath = new PathString("/Account/Login"),
Provider = new CookieAuthenticationProvider
{
// Enables the application to validate the security stamp when the user logs in.
// This is a security feature which is used when you change a password or add an external login to your account.
OnValidateIdentity =
SecurityStampValidator.OnValidateIdentity<ApplicationUserManager, ApplicationUser, Guid>(
TimeSpan.FromMinutes(int.Parse(WebConfigurationManager.AppSettings["RefreshInterval"])),
(manager, user) => manager.GenerateUserIdentityAsync(user),
claim => new Guid(claim.GetUserId())),
OnApplyRedirect = ctx =>
{
if (!IsAjaxRequest(ctx.Request))
{
ctx.Response.Redirect(ctx.RedirectUri);
}
}
}
});
}
}

Answer 1

After hours of investigation I eventually found the issue.
The issue was the number of claims being added for a user. Once we reduced the number of claims it started working again.

Answer 2

The most likely cause is that you're stuck in an error loop. If the authentication to the database where the users is stored is failing then you will get sent to the error page which will try to run the authentication again and fail and send you to the error page, again and again. Each pass it would append to the previous url eventually reaching this state.