IAM JSON policy elements: Condition

The Condition element (or Condition block) lets you specify conditions for when a policy is in effect. The Condition element is optional. In the Condition element, you build expressions in which you use condition operators (equal, less than, and others) to match the context keys and values in the policy against keys and values in the request context. To learn more about the request context, see Request.


"Condition" : { "{condition-operator}" : { "{condition-key}" : "{condition-value}" }}

The context key that you specify in a policy condition can be a global condition context key or a service-specific context key. Global condition context keys have the aws: prefix. Service-specific context keys have the service's prefix. For example, Amazon EC2 lets you write a condition using the ec2:InstanceType context key, which is unique to that service. To view service-specific IAM context keys with the iam: prefix, see IAM and Amazon STS condition context keys.

Context key names are not case-sensitive. For example, including the aws:SourceIP context key is equivalent to testing for AWS:SourceIp. Case-sensitivity of context key values depends on the condition operator that you use. For example, the following condition includes the StringEquals operator to make sure that only requests made by johndoe match. Users named JohnDoe are denied access.


"Condition" : { "StringEquals" : { "aws:username" : "johndoe" }}

The following condition uses the StringEqualsIgnoreCase operator to match users named johndoe or JohnDoe.


"Condition" : { "StringEqualsIgnoreCase" : { "aws:username" : "johndoe" }}

Some context keys support key–value pairs that allow you to specify part of the key name. Examples include the aws:RequestTag/tag-key context key, the Amazon KMS kms:EncryptionContext:encryption_context_key, and the ResourceTag/tag-key context key supported by multiple services.

If you use the ResourceTag/tag-key context key for a service such as Amazon EC2, then you must specify a key name for the tag-key.
Key names are not case-sensitive. This means that if you specify "aws:ResourceTag/TagKey1": "Value1" in the condition element of your policy, then the condition matches a resource tag key named either TagKey1 or tagkey1, but not both.
Amazon services that support these attributes might allow you to create multiple key names that differ only by case. For example, you might tag an Amazon EC2 instance with ec2=test1 and EC2=test2. When you use a condition such as "aws:ResourceTag/EC2": "test1" to allow access to that resource, the key name matches both tags, but only one value matches. This can result in unexpected condition failures.

Important

As a best practice, make sure that members of your account follow a consistent naming convention when naming key–value pair attributes. Examples include tags or Amazon KMS encryption contexts. You can enforce this using the aws:TagKeys context key for tagging, or the kms:EncryptionContextKeys for the Amazon KMS encryption context.

For a list of all of the condition operators and a description of how they work, see Condition operators.
Unless otherwise specified, all context keys can have multiple values. For a description of how to handle context keys that have multiple values, see Multivalued context keys.
For a list of all of the globally available context keys, see Amazon global condition context keys.
For condition context keys that are defined by each service, see Actions, Resources, and Condition Keys for Amazon Services.

The request context

When a principal makes a request to Amazon, Amazon gathers the request information into a request context. The information is used to evaluate and authorize the request. You can use the Condition element of a JSON policy to test specific context keys against the request context. For example, you can create a policy that uses the aws:CurrentTime context key to allow a user to perform actions within only a specific range of dates.

When a request is submitted, Amazon evaluates each context key in the policy and returns a value of true, false, not present, and occasionally null (an empty data string). A context key that is not present in the request is considered a mismatch. For example, the following policy allows removing your own multi-factor authentication (MFA) device, but only if you have signed in using MFA in the last hour (3,600 seconds).


{
    "Version": "2012-10-17",
    "Statement": {
        "Sid": "AllowRemoveMfaOnlyIfRecentMfa",
        "Effect": "Allow",
        "Action": [
            "iam:DeactivateMFADevice"
        ],
        "Resource": "arn:aws-cn:iam::*:user/${aws:username}",
        "Condition": {
            "NumericLessThanEquals": {"aws:MultiFactorAuthAge": "3600"}
        }
    }
}

The request context can return the following values:

True – If the requester signed in using MFA in the last one hour or less, then the condition returns true.
False – If the requester signed in using MFA more than one hour ago, then the condition returns false.
Not present – If the requester made a request using their IAM user access keys in the Amazon CLI or Amazon API, the key is not present. In this case, the key is not present, and it won't match.
Null – For context keys that are defined by the user, such as passing tags in a request, it is possible to include an empty string. In this case, the value in the request context is null. A null value might return true in some cases. For example, if you use the multivalued ForAllValues condition operator with the aws:TagKeys context key, you can experience unexpected results if the request context returns null. For more information, see aws:TagKeys and Multivalued context keys.

The condition block

The following example shows the basic format of a Condition element:


"Condition": {"StringLike": {"s3:prefix": ["janedoe/*"]}}

A value from the request is represented by a context key, in this case s3:prefix. The context key value is compared to a value that you specify as a literal value, such as janedoe/*. The type of comparison to make is specified by the condition operator (here, StringLike). You can create conditions that compare strings, dates, numbers, and more using typical Boolean comparisons such as equals, greater than, and less than. When you use string operators or ARN operators, you can also use a policy variable in the context key value. The following example includes the aws:username variable.


"Condition": {"StringLike": {"s3:prefix": ["${aws:username}/*"]}}

Under some circumstances, context keys can contain multiple values. For example, a request to Amazon DynamoDB might ask to return or update multiple attributes from a table. A policy for access to DynamoDB tables can include the dynamodb:Attributes context key, which contains all the attributes listed in the request. You can test the multiple attributes in the request against a list of allowed attributes in a policy by using set operators in the Condition element. For more information, see Multivalued context keys.

When the policy is evaluated during a request, Amazon replaces the key with the corresponding value from the request. (In this example, Amazon would use the date and time of the request.) The condition is evaluated to return true or false, which is then factored into whether the policy as a whole allows or denies the request.

Multiple values in a condition

A Condition element can contain multiple condition operators, and each condition operator can contain multiple context key-value pairs. The following figure illustrates this.

For more information, see Multivalued context keys.

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Condition operators