AuthenticationProviderService gets LDAP attributes
from confService and queries the LDAP server to
find values on user for specified attributes.
Added a Map<String, String> to Credentials named ldapAttrs
and a getLDAPAttributes() and setLDAPAttributes() to
manipulate ldapAttrs on credentials. Once
AuthenticationProviderService gets the values for the
LDAP attributes it sets ldapAttrs on the credentials object.
Added method getAttributes() in ConfigurationService to read environment property
LDAPGuacamoleProperties.LDAP_USER_ATTRIBUTES. These
attributes are arbitrary LDAP attributes that will
be mapped to the user in credentials and
tokens.