Issue 1058 | Gateway: allow nested fields verification

[IceKhan13]

Summary

Allow nested fields verification from auth API

Details and comments

Now if verification API has structure something like that

{
  "is_valid": true,
  "some": {
    "nested": {
      "field": true
    },
    "other": "bla"
  }
}

We can verify agains it with following settings:

"SETTINGS_TOKEN_AUTH_VERIFICATION_FIELD", "is_valid;some,nested,field"

---

Back compatible PR

Closes #1058

[psschwei]

How would we include other in the

"SETTINGS_TOKEN_AUTH_VERIFICATION_FIELD", "is_valid;some,nested,field"

block?

[IceKhan13]

If we need to check for other too

"SETTINGS_TOKEN_AUTH_VERIFICATION_FIELD", "is_valid;some,nested,field;some,other"

[akihikokuroda]

LGTM