public void setExternalId(String externalId) {
        this.externalId = externalId;
    }
<p>
A unique identifier that is used by third parties when assuming roles in
their customers' accounts. For each role that the third party can assume,
they should instruct their customers to ensure the role's trust policy
checks for the external ID that the third party generated. Each time the
third party assumes the role, they should pass the customer's external
ID. The external ID is useful in order to help third parties bind a role
to the customer who created it. For more information about the external
ID, see <a href=
"http://docs.aws.amazon.com/IAM/latest/UserGuide/id_roles_create_for-user_externalid.html"
>How to Use an External ID When Granting Access to Your AWS Resources to
a Third Party</a> in the <i>Using IAM</i>.
</p>

@param externalId
       A unique identifier that is used by third parties when assuming
       roles in their customers' accounts. For each role that the third
       party can assume, they should instruct their customers to ensure
       the role's trust policy checks for the external ID that the third
       party generated. Each time the third party assumes the role, they
       should pass the customer's external ID. The external ID is useful
       in order to help third parties bind a role to the customer who
       created it. For more information about the external ID, see <a
       href=
       "http://docs.aws.amazon.com/IAM/latest/UserGuide/id_roles_create_for-user_externalid.html"
       >How to Use an External ID When Granting Access to Your AWS
       Resources to a Third Party</a> in the <i>Using IAM</i>.
aws-java-sdk-core/src/main/java/com/amazonaws/auth/profile/internal/securitytoken/RoleInfo.java