[Openid-specs-fapi] Issue #528: C. PKCE Chosen Challenge Attack (openid/fapi)

[Nat]

New issue 528: C. PKCE Chosen Challenge Attack
https://bitbucket.org/openid/fapi/issues/528/c-pkce-chosen-challenge-attack

Nat Sakimura:

Need to address what to do with C. PKCE Chosen Challenge Attack in FAPI 2.0

For the attack, see [https://arxiv.org/pdf/1901.11520.pdf](https://arxiv.org/pdf/1901.11520.pdf)