Setting TYK_GW_HASHKEYFUNCTION changes key format

[jakub-bochenski]

Branch/Environment/Version

• Branch/Version: v5.1
• Environment: On-prem

Describe the bug
This is an unexpected and undocumented behaviour

If I only set TYK_GW_HASHKEYS=true the keys generated by tyk are of the form: 123@example.com1a4704c4c6f8456b9a859041e05a09d6

If I set TYK_GW_HASHKEYFUNCTION to any value (murmur64, murmur128, sha256) the returned key is now a base64 encoded json, e.g. eyJvcmciOiIxMjNAZXhhbXBsZS5jb20iLCJpZCI6Ijk5NzhkZDk0MGNkMzQ5YmNhZWY3YmQyMDQxNGY3YmMyIiwiaCI6InNoYTI1NiJ9

Which when decoded is

{"org":"123@example.com","id":"9978dd940cd349bcaef7bd20414f7bc2","h":"sha256"}

Reproduction steps
Set TYK_GW_HASHKEYFUNCTION to any value

Actual behavior
Key format changes

Expected behavior
Key format doesn't change

Additional context
This significantly increases the key size, which is a concern given that each API request includes in in the header.

[jakub-bochenski]

Was able to find the description here #1753

[jakub-bochenski]

This also makes the loggin statement useless as the key suffix is always one of the three key="****fQ== or key="****In0=" or key="****NiJ9"

e.g.

time="Oct 04 12:41:09" level=info msg="Key rate limit exceeded." api_id=foo api_name="foo" key="****In0=" mw=RateLimitAndQuotaCheck org_id=default origin=162.158.102.30 path=/foo