Why does @Html.AntiForgeryToken() generate different tokens in same response?

Question

A single Razor view contains several forms, each with its own call to @Html.AntiForgeryToken()

<form id="f1">
    @Html.AntiForgeryToken()
</form>

<form id="f2">
    @Html.AntiForgeryToken()
</form>

As I understand it, both of these anti forgery tokens should be the same.

<form id="f1">
    <input name="__RequestVerificationToken" type="hidden" value="duVT4VtiYybun-61lnSY1ol__qBwawnELooyqT5OSrCJrvcHvDs_Nr9GLxNxwvBaI4hUcKZVkm6mDEmH2UqNorHD1FnJbKJQLWe8Su_dhy_nnGGl5GhqqC3yRGzcxbBM0" />
</form>

<form id="f2">
    <input name="__RequestVerificationToken" type="hidden" value="ZMISz3IWHU_HCKP4FppDQ5lvzoYhlQGhN1cmzKBPz4OgDzyqSUK3Q1dqvw1uHsb4eNyd9U3AbFcnW8tR7g1QS8Dyhp0tFc-ee1sfDAOqbLCcgd3PDnLCbXx09pnPREaq0" />
</form>

Why are the values different?

Surely they should be the same, because they are sent in the same Response from the server?
The documentation says nothing about calling it once only.

Answer 1

The Anti-Forgery token is not compared directly - the server has to unprotect it first and compare the protected data inside. Having different protected tokens doesn't necessarily mean they contain differing data.

What the System.Web.Helpers.AntiXsrf.TokenValidator compares is the SecurityToken inside the decrypted AntiForgeryToken instances. These instances, however, also contain an AdditionalData field, a UserName field and a ClaimUid field.

Also, the SecurityToken inside the AntiForgeryToken is directly copied from the (current if it is valid, else the freshly generated) AntiForgery cookie inside AntiForgeryWorker.

Given that all that data is serialized, encrypted then encoded, you may have variances in the protected token due to differences between the AdditionalData between tokens or it is likely due to a pseudorandom nonce used in the encryption process (which it likely uses, since I can test 2 completely different tokens as valid against the same cookie).