HTTPCLIENT-2078: Log debug message when no credentials for given auth scope are found

This closes #251
diff --git a/httpclient5/src/main/java/org/apache/hc/client5/http/impl/auth/BasicScheme.java b/httpclient5/src/main/java/org/apache/hc/client5/http/impl/auth/BasicScheme.java
index 81b015a..427df1c 100644
--- a/httpclient5/src/main/java/org/apache/hc/client5/http/impl/auth/BasicScheme.java
+++ b/httpclient5/src/main/java/org/apache/hc/client5/http/impl/auth/BasicScheme.java
@@ -55,6 +55,8 @@
 import org.apache.hc.core5.http.NameValuePair;
 import org.apache.hc.core5.http.protocol.HttpContext;
 import org.apache.hc.core5.util.Args;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
  * Basic authentication scheme as defined in RFC 2617.
@@ -66,6 +68,8 @@
 
     private static final long serialVersionUID = -1931571557597830536L;
 
+    private static final Logger LOG = LoggerFactory.getLogger(BasicScheme.class);
+
     private final Map<String, String> paramMap;
     private transient Charset charset;
     private transient ByteArrayBuilder buffer;
@@ -141,13 +145,16 @@
         Args.notNull(host, "Auth host");
         Args.notNull(credentialsProvider, "CredentialsProvider");
 
+        final AuthScope authScope = new AuthScope(host, getRealm(), getName());
         final Credentials credentials = credentialsProvider.getCredentials(
-                new AuthScope(host, getRealm(), getName()), context);
+                authScope, context);
         if (credentials != null) {
             this.username = credentials.getUserPrincipal().getName();
             this.password = credentials.getPassword();
             return true;
         }
+
+        LOG.debug("No credentials found for auth scope [{}]", authScope);
         this.username = null;
         this.password = null;
         return false;
diff --git a/httpclient5/src/main/java/org/apache/hc/client5/http/impl/auth/DigestScheme.java b/httpclient5/src/main/java/org/apache/hc/client5/http/impl/auth/DigestScheme.java
index d9b5177..7353e6f 100644
--- a/httpclient5/src/main/java/org/apache/hc/client5/http/impl/auth/DigestScheme.java
+++ b/httpclient5/src/main/java/org/apache/hc/client5/http/impl/auth/DigestScheme.java
@@ -64,6 +64,8 @@
 import org.apache.hc.core5.http.protocol.HttpContext;
 import org.apache.hc.core5.util.Args;
 import org.apache.hc.core5.util.CharArrayBuffer;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
  * Digest authentication scheme as defined in RFC 2617.
@@ -83,6 +85,8 @@
 
     private static final long serialVersionUID = 3883908186234566916L;
 
+    private static final Logger LOG = LoggerFactory.getLogger(DigestScheme.class);
+
     /**
      * Hexa values used when creating 32 character long digest in HTTP DigestScheme
      * in case of authentication.
@@ -173,13 +177,16 @@
         Args.notNull(host, "Auth host");
         Args.notNull(credentialsProvider, "CredentialsProvider");
 
+        final AuthScope authScope = new AuthScope(host, getRealm(), getName());
         final Credentials credentials = credentialsProvider.getCredentials(
-                new AuthScope(host, getRealm(), getName()), context);
+                authScope, context);
         if (credentials != null) {
             this.username = credentials.getUserPrincipal().getName();
             this.password = credentials.getPassword();
             return true;
         }
+
+        LOG.debug("No credentials found for auth scope [{}]", authScope);
         this.username = null;
         this.password = null;
         return false;
diff --git a/httpclient5/src/main/java/org/apache/hc/client5/http/impl/auth/NTLMScheme.java b/httpclient5/src/main/java/org/apache/hc/client5/http/impl/auth/NTLMScheme.java
index 1b1beb3..53c4a7b 100644
--- a/httpclient5/src/main/java/org/apache/hc/client5/http/impl/auth/NTLMScheme.java
+++ b/httpclient5/src/main/java/org/apache/hc/client5/http/impl/auth/NTLMScheme.java
@@ -41,6 +41,8 @@
 import org.apache.hc.core5.http.HttpRequest;
 import org.apache.hc.core5.http.protocol.HttpContext;
 import org.apache.hc.core5.util.Args;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
  * NTLM is a proprietary authentication scheme developed by Microsoft
@@ -50,6 +52,8 @@
  */
 public final class NTLMScheme implements AuthScheme {
 
+    private static final Logger LOG = LoggerFactory.getLogger(NTLMScheme.class);
+
     enum State {
         UNINITIATED,
         CHALLENGE_RECEIVED,
@@ -126,12 +130,15 @@
         Args.notNull(host, "Auth host");
         Args.notNull(credentialsProvider, "CredentialsProvider");
 
+        final AuthScope authScope = new AuthScope(host, null, getName());
         final Credentials credentials = credentialsProvider.getCredentials(
-                new AuthScope(host, null, getName()), context);
+                authScope, context);
         if (credentials instanceof NTCredentials) {
             this.credentials = (NTCredentials) credentials;
             return true;
         }
+
+        LOG.debug("No credentials found for auth scope [{}]", authScope);
         return false;
     }