Changes to Validate credentials

the request property login became required

the request property password became required

added the non-success response with the status 400

added the optional property description to the response with the 200 status

added the optional property description to the response with the 401 status

added the optional property error to the response with the 200 status

added the optional property error to the response with the 401 status

api operation id externalAuthentication was added

added the non-success response with the status 401

removed the optional property description from the response with the 200 status

removed the optional property error from the response with the 200 status

api operation id externalAuthentication removed and replaced with

the request property login became optional

the request property password became optional

removed the non-success response with the status 400

removed the non-success response with the status 401