A computer-implemented method for processing authentication of a consumer via a computer at a centralized merchant authentication processing system, MAPS, using one of a plurality of different types of payment instruments to conduct a commercial transaction over a communications network with a server operated by an online merchant, wherein the server includes a thin client operable to link information with the MAPS upon demand and operable to format name/value pairs to a required MAPS message format and to securely communicate the message to the MAPS, wherein the payment instrument being used is either enrolled in or not enrolled in an authentication program conforming to one of a plurality of authentication protocols prescribed for the respective plurality of different types of payment instruments by payment networks (70, 72, 74, 76, 78) supporting the same, wherein the MAPS comprises a connectivity layer that sits on top a message distribution layer that sits on top a plug-in layer and an external connection layer, the method comprising: (a) obtaining at the server payment information for the transaction from the consumer and forwarding the payment information to the MAPS using the thin client, said payment information including a number identifying the particular payment instrument being used; (b) determining at the MAPS the type of payment instrument being used from the payment information, wherein the plug-in layer of the MAPS includes a plurality of individual authentication initiative plug-in components operable to listen to the message distribution layer for a specific message type, wherein a respective plug-in component is activated by the message distribution layer that sends messages to the specified plug-in component based upon the type of payment instrument being used for the transaction being processed; (c) obtaining at the MAPS an authentication determination from one of the payment networks (70, 72, 74, 76, 78) for the transaction in accordance with the authentication protocols prescribed for the determined type of payment instrument being used; and, (d) the MAPS returning the obtained authentication determination to the server operated by the merchant. (a) obtaining at the server payment information for the transaction from the consumer and forwarding the payment information to the MAPS using the thin client, said payment information including a number identifying the particular payment instrument being used; (b) determining at the MAPS the type of payment instrument being used from the payment information, wherein the plug-in layer of the MAPS includes a plurality of individual authentication initiative plug-in components operable to listen to the message distribution layer for a specific message type, wherein a respective plug-in component is activated by the message distribution layer that sends messages to the specified plug-in component based upon the type of payment instrument being used for the transaction being processed; (c) obtaining at the MAPS an authentication determination from one of the payment networks (70, 72, 74, 76, 78) for the transaction in accordance with the authentication protocols prescribed for the determined type of payment instrument being used; and, (d) the MAPS returning the obtained authentication determination to the server operated by the merchant.