sqlmap cannot just avoid the login, but if you know the credentials you can try the switches --auth-cred name:password --auth-type (Basic, or Digest ,or NTLM)
if is an http autenticati on,
try also --dbms-cred user:password
if you need to authenticate into the DB. that will work only if you know the credentials.
but im not sure thats your case, mmh maybe an sqlmap output will help