Blazor Custom Route Constraints

I am trying to use custom route constraint in Blazor, similar to how it currently works for both razor pages and MVC routes:

services.AddRouting(options =>
{
    options.ConstraintMap.Add("customName", typeof(MyCustomConstraint));
});

… but it appears that blazor route constraints do not consider any custom constraints that have been registered:

https://github.com/dotnet/aspnetcore/blob/af7c0cc2a2f944811041b55f9b4e0ae6cc948fd7/src/Components/Components/src/Routing/RouteConstraint.cs#L57-L85

So I instead encounter the ArgumentException, “Unsupported constraint ‘{constraint}’ in route ‘{template}’.”.

It would be ideal if RouteConstraint could be modified to reference RouteOptions.ContraintMap as the other routing engines do. Alternatively, needing to use some Blazor-specific registration method to register constraints only for Blazor would also be acceptable.

[kyletinsley]

Regex route constraints would be wonderful. Trying to constrain a string route parameter to a finite list of string values and want to 404 otherwise.

[Alerinos]

@pranavkm I would like to remind you of this, it is quite an important and useful thing.