feat: slf4j based logging

Author: augi

core/build.gradle

@@ -1,5 +1,6 @@
 archivesBaseName = 'grpc-java-jwt'
 
 dependencies {
-    compile "io.grpc:grpc-core:$grpcVersion"    
+    compile "io.grpc:grpc-core:$grpcVersion"
+    compile "org.slf4j:slf4j-api:1.7.26"
 }

core/src/main/java/com/avast/grpc/jwt/client/JwtCallCredentials.java

@@ -5,8 +5,11 @@
 import io.grpc.Metadata;
 import io.grpc.Status;
 import java.util.concurrent.Executor;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 public abstract class JwtCallCredentials extends CallCredentials {
+  private static Logger LOGGER = LoggerFactory.getLogger(JwtCallCredentials.class);
 
   public static JwtCallCredentials synchronous(SynchronousJwtTokenProvider tokenProvider) {
     return new Synchronous(tokenProvider);
@@ -30,10 +33,9 @@ protected void applyToken(MetadataApplier applier, String jwtToken) {
   }
 
   protected void applyFailure(MetadataApplier applier, Throwable e) {
-    applier.fail(
-        Status.UNAUTHENTICATED
-            .withDescription("An exception when obtaining JWT token")
-            .withCause(e));
+    String msg = "An exception when obtaining JWT token";
+    LOGGER.error(msg, e);
+    applier.fail(Status.UNAUTHENTICATED.withDescription(msg).withCause(e));
   }
 
   public static class Synchronous extends JwtCallCredentials {

core/src/main/java/com/avast/grpc/jwt/server/JwtServerInterceptor.java

@@ -2,8 +2,12 @@
 
 import com.avast.grpc.jwt.Constants;
 import io.grpc.*;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 public class JwtServerInterceptor<T> implements ServerInterceptor {
+  private static Logger LOGGER = LoggerFactory.getLogger(JwtServerInterceptor.class);
+
   public final io.grpc.Context.Key<T> AccessTokenContextKey = Context.key("AccessToken");
 
   private static final String AUTH_HEADER_PREFIX = "Bearer ";
@@ -19,33 +23,30 @@ public <ReqT, RespT> ServerCall.Listener<ReqT> interceptCall(
       ServerCall<ReqT, RespT> call, Metadata headers, ServerCallHandler<ReqT, RespT> next) {
     String authHeader = headers.get(Constants.AuthorizationMetadataKey);
     if (authHeader == null) {
-      call.close(
-          Status.UNAUTHENTICATED.withDescription(
-              Constants.AuthorizationMetadataKey.name() + " header not found"),
-          new Metadata());
+      String msg = Constants.AuthorizationMetadataKey.name() + " header not found";
+      LOGGER.warn(msg);
+      call.close(Status.UNAUTHENTICATED.withDescription(msg), new Metadata());
       return new ServerCall.Listener<ReqT>() {};
     }
     if (!authHeader.startsWith(AUTH_HEADER_PREFIX)) {
-      call.close(
-          Status.UNAUTHENTICATED.withDescription(
-              Constants.AuthorizationMetadataKey.name()
-                  + " header does not start with "
-                  + AUTH_HEADER_PREFIX),
-          new Metadata());
+      String msg =
+          Constants.AuthorizationMetadataKey.name()
+              + " header does not start with "
+              + AUTH_HEADER_PREFIX;
+      LOGGER.warn(msg);
+      call.close(Status.UNAUTHENTICATED.withDescription(msg), new Metadata());
       return new ServerCall.Listener<ReqT>() {};
     }
     T token;
     try {
       token = tokenParser.parseToValid(authHeader.substring(AUTH_HEADER_PREFIX.length()));
     } catch (Exception e) {
-      call.close(
-          Status.UNAUTHENTICATED
-              .withDescription(
-                  Constants.AuthorizationMetadataKey.name()
-                      + " header validation failed: "
-                      + e.getMessage())
-              .withCause(e),
-          new Metadata());
+      String msg =
+          Constants.AuthorizationMetadataKey.name()
+              + " header validation failed: "
+              + e.getMessage();
+      LOGGER.warn(msg, e);
+      call.close(Status.UNAUTHENTICATED.withDescription(msg).withCause(e), new Metadata());
       return new ServerCall.Listener<ReqT>() {};
     }
     return Contexts.interceptCall(