Make MIN_SPRING_VERSION Dynamic

Fixes: gh-5065

# Conflicts:
#	core/src/main/java/org/springframework/security/core/SpringSecurityCoreVersion.java

core/spring-security-core.gradle

@@ -34,6 +34,17 @@ dependencies {
 	testRuntime 'org.hsqldb:hsqldb'
 }
 
+task springVersion(type: versions.VersionsResourceTasks) {
+	versionsFile = file("${buildDir}/versions/spring-security.versions")
+	versions = { project.dependencyManagement.managedVersions }
+}
+
+tasks.processResources {
+	into('META-INF') {
+		from project.tasks.springVersion.outputs
+	}
+}
+
 tasks.jar.from { includeProject.sourceSets.main.output }
 
 tasks.sourcesJar.from {includeProject.sourceSets.main.java}

core/src/main/java/org/springframework/security/core/SpringSecurityCoreVersion.java

@@ -20,6 +20,9 @@ import org.apache.commons.logging.LogFactory;
 
 import org.springframework.core.SpringVersion;
 
+import java.io.IOException;
+import java.util.Properties;
+
 /**
  * Internal class used for checking version compatibility in a deployed application.
  *
@@ -40,7 +43,7 @@ public class SpringSecurityCoreVersion {
 	 */
 	public static final long SERIAL_VERSION_UID = 500L;
 
-	static final String MIN_SPRING_VERSION = "5.0.5.RELEASE";
+	static final String MIN_SPRING_VERSION = getSpringVersion();
 
 	static {
 		performVersionChecks();
@@ -64,6 +67,9 @@ public class SpringSecurityCoreVersion {
 	 * @param minSpringVersion
 	 */
 	private static void performVersionChecks(String minSpringVersion) {
+		if (minSpringVersion == null) {
+			return;
+		}
 		// Check Spring Compatibility
 		String springVersion = SpringVersion.getVersion();
 		String version = getVersion();
@@ -95,4 +101,18 @@ public class SpringSecurityCoreVersion {
 		}
 		return Boolean.getBoolean(DISABLE_CHECKS);
 	}
+
+	/**
+	 * Loads the spring version or null if it cannot be found.
+	 * @return
+	 */
+	private static String getSpringVersion() {
+		Properties properties = new Properties();
+		try {
+			properties.load(SpringSecurityCoreVersion.class.getClassLoader().getResourceAsStream("META-INF/spring-security.versions"));
+		} catch (IOException e) {
+			return null;
+		}
+		return properties.getProperty("org.springframework:spring-core");
+	}
 }