GUACAMOLE-773: Add exclusions as necessary to force correct dependency versions. Remove exclusions that are no longer necessary.

extensions/guacamole-auth-saml/pom.xml

@@ -75,13 +75,24 @@
             <artifactId>java-saml</artifactId>
             <version>2.6.0</version>
             <exclusions>
+
+                <!-- Force consistent version of commons-codec (see below) -->
                 <exclusion>
-                    <groupId>org.slf4j</groupId>
-                    <artifactId>slf4j-api</artifactId>
+                    <groupId>commons-codec</groupId>
+                    <artifactId>commons-codec</artifactId>
                 </exclusion>
+
             </exclusions>
         </dependency>
 
+        <!-- Force single, specific version of commons-codec (multiple
+            dependencies reference multiple versions of this). -->
+        <dependency>
+            <groupId>commons-codec</groupId>
+            <artifactId>commons-codec</artifactId>
+            <version>1.15</version>
+        </dependency>
+
     </dependencies>
 
 </project>