diff --git a/httpclient/src/main/java/org/apache/http/auth/AUTH.java b/httpclient/src/main/java/org/apache/http/auth/AUTH.java
index 0c68cffa3..e36989026 100644
--- a/httpclient/src/main/java/org/apache/http/auth/AUTH.java
+++ b/httpclient/src/main/java/org/apache/http/auth/AUTH.java
@@ -31,12 +31,15 @@
 
 package org.apache.http.auth;
 
+import net.jcip.annotations.Immutable;
+
 /**
  * Constants and static helpers related to the HTTP authentication.
  * 
  *
  * @since 4.0
  */
+@Immutable
 public final class AUTH {
 
     /**
diff --git a/httpclient/src/main/java/org/apache/http/auth/AuthSchemeRegistry.java b/httpclient/src/main/java/org/apache/http/auth/AuthSchemeRegistry.java
index 12ce45621..bb8983865 100644
--- a/httpclient/src/main/java/org/apache/http/auth/AuthSchemeRegistry.java
+++ b/httpclient/src/main/java/org/apache/http/auth/AuthSchemeRegistry.java
@@ -36,6 +36,9 @@ import java.util.List;
 import java.util.Locale;
 import java.util.Map;
 
+import net.jcip.annotations.GuardedBy;
+import net.jcip.annotations.ThreadSafe;
+
 import org.apache.http.params.HttpParams;
 
 /**
@@ -47,8 +50,10 @@ import org.apache.http.params.HttpParams;
  * @version $Revision$
  * @since 4.0
  */
+@ThreadSafe
 public final class AuthSchemeRegistry {
 
+    @GuardedBy("this")
     private final Map<String,AuthSchemeFactory> registeredSchemes;
     
     public AuthSchemeRegistry() {
diff --git a/httpclient/src/main/java/org/apache/http/auth/AuthScope.java b/httpclient/src/main/java/org/apache/http/auth/AuthScope.java
index 5eb6a4de8..c71c8bce0 100644
--- a/httpclient/src/main/java/org/apache/http/auth/AuthScope.java
+++ b/httpclient/src/main/java/org/apache/http/auth/AuthScope.java
@@ -32,6 +32,8 @@ package org.apache.http.auth;
 
 import java.util.Locale;
 
+import net.jcip.annotations.Immutable;
+
 import org.apache.http.util.LangUtils;
 
 /** 
@@ -42,6 +44,7 @@ import org.apache.http.util.LangUtils;
  * 
  * @since 4.0
  */
+@Immutable
 public class AuthScope {
     
     /** 
diff --git a/httpclient/src/main/java/org/apache/http/auth/AuthState.java b/httpclient/src/main/java/org/apache/http/auth/AuthState.java
index 5a848a6a0..70bdcc3f9 100644
--- a/httpclient/src/main/java/org/apache/http/auth/AuthState.java
+++ b/httpclient/src/main/java/org/apache/http/auth/AuthState.java
@@ -30,6 +30,8 @@
 
 package org.apache.http.auth;
 
+import net.jcip.annotations.NotThreadSafe;
+
 
 /**
  * This class provides detailed information about the state of the
@@ -38,6 +40,7 @@ package org.apache.http.auth;
  *
  * @since 4.0
  */
+@NotThreadSafe
 public class AuthState {
 
     /** Actual authentication scheme */
diff --git a/httpclient/src/main/java/org/apache/http/auth/AuthenticationException.java b/httpclient/src/main/java/org/apache/http/auth/AuthenticationException.java
index 0c437176b..b3d9bfed9 100644
--- a/httpclient/src/main/java/org/apache/http/auth/AuthenticationException.java
+++ b/httpclient/src/main/java/org/apache/http/auth/AuthenticationException.java
@@ -30,6 +30,8 @@
 
 package org.apache.http.auth;
 
+import net.jcip.annotations.Immutable;
+
 import org.apache.http.ProtocolException;
 
 /**
@@ -38,6 +40,7 @@ import org.apache.http.ProtocolException;
  * 
  * @since 4.0
  */
+@Immutable
 public class AuthenticationException extends ProtocolException {
 
     private static final long serialVersionUID = -6794031905674764776L;
diff --git a/httpclient/src/main/java/org/apache/http/auth/BasicUserPrincipal.java b/httpclient/src/main/java/org/apache/http/auth/BasicUserPrincipal.java
index 92c49aaea..6f7c7a11e 100644
--- a/httpclient/src/main/java/org/apache/http/auth/BasicUserPrincipal.java
+++ b/httpclient/src/main/java/org/apache/http/auth/BasicUserPrincipal.java
@@ -32,6 +32,8 @@ package org.apache.http.auth;
 
 import java.security.Principal;
 
+import net.jcip.annotations.Immutable;
+
 import org.apache.http.util.LangUtils;
 
 /**
@@ -40,6 +42,7 @@ import org.apache.http.util.LangUtils;
  * 
  * @since 4.0
  */
+@Immutable
 public final class BasicUserPrincipal implements Principal {
 
     private final String username;
diff --git a/httpclient/src/main/java/org/apache/http/auth/InvalidCredentialsException.java b/httpclient/src/main/java/org/apache/http/auth/InvalidCredentialsException.java
index cb10b3b77..8d26d3b8e 100644
--- a/httpclient/src/main/java/org/apache/http/auth/InvalidCredentialsException.java
+++ b/httpclient/src/main/java/org/apache/http/auth/InvalidCredentialsException.java
@@ -30,6 +30,8 @@
 
 package org.apache.http.auth;
 
+import net.jcip.annotations.Immutable;
+
 /**
  * Authentication credentials required to respond to a authentication 
  * challenge are invalid
@@ -37,6 +39,7 @@ package org.apache.http.auth;
  * 
  * @since 4.0
  */
+@Immutable
 public class InvalidCredentialsException extends AuthenticationException {
 
     private static final long serialVersionUID = -4834003835215460648L;
diff --git a/httpclient/src/main/java/org/apache/http/auth/MalformedChallengeException.java b/httpclient/src/main/java/org/apache/http/auth/MalformedChallengeException.java
index 48bb2a5f4..fb3b6a705 100644
--- a/httpclient/src/main/java/org/apache/http/auth/MalformedChallengeException.java
+++ b/httpclient/src/main/java/org/apache/http/auth/MalformedChallengeException.java
@@ -30,6 +30,8 @@
 
 package org.apache.http.auth;
 
+import net.jcip.annotations.Immutable;
+
 import org.apache.http.ProtocolException;
 
 /**
@@ -39,6 +41,7 @@ import org.apache.http.ProtocolException;
  * 
  * @since 4.0
  */
+@Immutable
 public class MalformedChallengeException extends ProtocolException {
 
     private static final long serialVersionUID = 814586927989932284L;
diff --git a/httpclient/src/main/java/org/apache/http/auth/NTCredentials.java b/httpclient/src/main/java/org/apache/http/auth/NTCredentials.java
index 9bd19a39b..88fdd2f3f 100644
--- a/httpclient/src/main/java/org/apache/http/auth/NTCredentials.java
+++ b/httpclient/src/main/java/org/apache/http/auth/NTCredentials.java
@@ -33,6 +33,8 @@ package org.apache.http.auth;
 import java.security.Principal;
 import java.util.Locale;
 
+import net.jcip.annotations.Immutable;
+
 import org.apache.http.util.LangUtils;
 
 /** {@link Credentials} specific to the Windows platform.
@@ -40,6 +42,7 @@ import org.apache.http.util.LangUtils;
  * 
  * @since 2.0
  */
+@Immutable
 public class NTCredentials implements Credentials {
 
     /** The user principal  */
diff --git a/httpclient/src/main/java/org/apache/http/auth/NTUserPrincipal.java b/httpclient/src/main/java/org/apache/http/auth/NTUserPrincipal.java
index 512c6c76a..872ca6318 100644
--- a/httpclient/src/main/java/org/apache/http/auth/NTUserPrincipal.java
+++ b/httpclient/src/main/java/org/apache/http/auth/NTUserPrincipal.java
@@ -33,6 +33,8 @@ package org.apache.http.auth;
 import java.security.Principal;
 import java.util.Locale;
 
+import net.jcip.annotations.Immutable;
+
 import org.apache.http.util.LangUtils;
 
 /**  NT (MS Windows specific) user principal used for HTTP authentication
@@ -40,6 +42,7 @@ import org.apache.http.util.LangUtils;
  * 
  * @since 4.0
  */
+@Immutable
 public class NTUserPrincipal implements Principal {
 
     private final String username;
diff --git a/httpclient/src/main/java/org/apache/http/auth/UsernamePasswordCredentials.java b/httpclient/src/main/java/org/apache/http/auth/UsernamePasswordCredentials.java
index e28bb9781..3987bbd22 100644
--- a/httpclient/src/main/java/org/apache/http/auth/UsernamePasswordCredentials.java
+++ b/httpclient/src/main/java/org/apache/http/auth/UsernamePasswordCredentials.java
@@ -32,6 +32,8 @@ package org.apache.http.auth;
 
 import java.security.Principal;
 
+import net.jcip.annotations.Immutable;
+
 import org.apache.http.util.LangUtils;
 
 /**
@@ -43,11 +45,12 @@ import org.apache.http.util.LangUtils;
  *
  * @since 4.0
  */
+@Immutable
 public class UsernamePasswordCredentials implements Credentials {
 
     private final BasicUserPrincipal principal;
     private final String password;
-     
+    
     /**
      * The constructor with the username and password combined string argument.
      *