Returns the Amazon Resource Name (ARN) for the CA certificate. For example: { "Fn::GetAtt": ["MyCACertificate", "Arn"] } A value similar to the following is returned: arn:aws:iot:us-east-1:123456789012:cacert/a6be6b84559801927e35a8f901fae08b5971d78d1562e29504ff9663b276a5f5