Adds the extension grant validator.
public static IIdentityServerBuilder AddExtensionGrantValidator<T>(IIdentityServerBuilder builder) where T : IdentityServer4.Validation.IExtensionGrantValidator
                - Returns:
 - IIdentityServerBuilder
 
Parameters
builder
                                IIdentityServerBuilder
The builder.
Type Parameters
T
                            IdentityServer4.Validation.IExtensionGrantValidator