1. A computer-implemented method comprising: receiving, by one or more processors, an access request from a client computer for access to a protected resource stored on a target server; forwarding, by the one or more processors, the access request to the target server; receiving, by the one or more processors, an access response from the target server, wherein the access response is a credential form including credential fields required to access the protected resource; injecting, by the one or more processors, a credential field tag into each required credential field; sending, by the one or more processors, the tagged credential form to the client computer; receiving, by the one or more processors, a tagged credential form from the client computer including tagged credentials in the required credential fields with the credential field tags; replacing, by the one or more processors, the tagged credentials with target credentials mapped by the credential field tags, wherein the target credentials are stored in a protected data store; sending, by the one or more processors, the target credentials to the target server; updating, by the one or more processors, the target credentials and storing the updated target credentials in a protected data store without client intervention, in response to the target credentials being invalid; and allowing, by the one or more processors, the client computer to access the protected resource, in response to the target server validating the target credentials.