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StringNotEqualsIfExists

StringNotEqualsIfExists

StringNotEqualsIfExists compares a string in a request to a list of strings in your policy. The comparison is case sensitive.

To match a request, the context key can be absent, but if present it must NOT match any of the strings in your policy.

You can use policy variables in the value of this operator.

So you know:

StringNotEqualsIfExists behaves exactly the same as StringNotEquals. "Negative" operators such as StringNotEquals already match requests if the key is not present so the IfExists suffix has no effect.

There is no harm in adding IfExists to StringNotEquals; it probably makes the intent more clear. We know you already knew this, but put this message in for everyone else. 😉

StringNotEqualsIfExists in an Allow Statement

Given the Policy Condition: 
"StringNotEqualsIfExists": {
  "aws:RequestTag/DataClass": [
    "public",
    "internal"
  ]
}
When the Request Context has:
aws:RequestTag/DataClass: null
Then the result is:
Allowed Allowed Assuming no explicit Deny elsewhere
Given the Policy Condition: 
"StringNotEqualsIfExists": {
  "aws:RequestTag/DataClass": [
    "public",
    "internal"
  ]
}
When the Request Context has:
aws:RequestTag/DataClass: private
Then the result is:
Allowed Allowed Assuming no explicit Deny elsewhere
Given the Policy Condition: 
"StringNotEqualsIfExists": {
  "aws:RequestTag/DataClass": [
    "public",
    "internal"
  ]
}
When the Request Context has:
aws:RequestTag/DataClass: public
Then the result is:
Not Allowed Not Allowed Statement does not apply

StringNotEqualsIfExists in a Deny Statement

Given the Policy Condition: 
"StringNotEqualsIfExists": {
  "aws:RequestTag/DataClass": [
    "public",
    "internal"
  ]
}
When the Request Context has:
aws:RequestTag/DataClass: null
Then the result is:
Denied Denied
Given the Policy Condition: 
"StringNotEqualsIfExists": {
  "aws:RequestTag/DataClass": [
    "public",
    "internal"
  ]
}
When the Request Context has:
aws:RequestTag/DataClass: private
Then the result is:
Denied Denied
Given the Policy Condition: 
"StringNotEqualsIfExists": {
  "aws:RequestTag/DataClass": [
    "public",
    "internal"
  ]
}
When the Request Context has:
aws:RequestTag/DataClass: public
Then the result is:
Not Denied Not Denied May be allowed by another statement