Merge pull request oauth-wg#125 from oauth-wg/clarify-logging

clarified logging recommendation

draft-ietf-oauth-transaction-tokens.md

@@ -636,7 +636,7 @@ and if so their values need to be obfuscated. For example, originating IP addres
 protected through some obfuscation method (e.g. salted SHA256).
 
 ## Logging
-Txn-Tokens SHOULD NOT be logged if they contain Personally Identifiable Information (PII). What constitutes PII depends upon the use case, but in some cases even an email address (which could be a `sub` value) can be protected PII, which should not be logged.
+Complete Txn-Tokens must not be logged verbatim. This is in order to prevent replay of tokens or leakage of PII or other sensitive information via log files. A hash of the Txn-Token may be logged to allow for correlation with the log files of the Txn-Token Service that records issued tokens. Alternatively the JWS payload of a Txn-Token may be logged after the signature has been removed. If the Txn-Token contains PII, then care should be taken in logging the content of the Txn-Token so that the PII does not get logged.
 
 # IANA Considerations {#IANA}