An image forming apparatus that is capable of executing authentication processing improved in security of a command including authentication information, which is received over a network from an external apparatus. A CPU receives a command including authentication information via a network. The CPU determines whether or not authentication information included in the received command is a hash value or an encrypted value. The CPU causes processing in accordance with the received command to be executed depending on authentication performed based on the authentication information when it is determined that the authentication information is a hash value or an encrypted value, and causes the processing not to be executed when it is determined that the authentication information is not a hash value or an encrypted value.