The SECURITY_IMPERSONATION_LEVEL enumeration defines a set of values that specify security impersonation levels as specified in [MS-LSAD] section 2.2.3.5.

 typedef  enum _SECURITY_IMPERSONATION_LEVEL
 {
   SecurityAnonymous = 0,
   SecurityIdentification = 1,
   SecurityImpersonation = 2,
   SecurityDelegation = 3
 } SECURITY_IMPERSONATION_LEVEL,
  *PSECURITY_IMPERSONATION_LEVEL;

Individual value semantics are specified in [MS-LSAD] section 2.2.3.5.