public void setPrincipal(String principal) {
        this.principal = principal;
    }
<p>
The principal. Valid principals are CertificateArn
(arn:aws:iot:<i>region</i>:<i>accountId</i>:cert/<i>certificateId</i>), thingGroupArn
(arn:aws:iot:<i>region</i>:<i>accountId</i>:thinggroup/<i>groupName</i>) and CognitoId (<i>region</i>:<i>id</i>).
</p>

@param principal
       The principal. Valid principals are CertificateArn
       (arn:aws:iot:<i>region</i>:<i>accountId</i>:cert/<i>certificateId</i>), thingGroupArn
       (arn:aws:iot:<i>region</i>:<i>accountId</i>:thinggroup/<i>groupName</i>) and CognitoId
       (<i>region</i>:<i>id</i>).
aws-java-sdk-iot/src/main/java/com/amazonaws/services/iot/model/TestAuthorizationRequest.java