diff --git a/src/main/java/moe/yushi/authlibinjector/AuthlibInjector.java b/src/main/java/moe/yushi/authlibinjector/AuthlibInjector.java
index 972e741..499b0b1 100644
--- a/src/main/java/moe/yushi/authlibinjector/AuthlibInjector.java
+++ b/src/main/java/moe/yushi/authlibinjector/AuthlibInjector.java
@@ -3,12 +3,16 @@ package moe.yushi.authlibinjector;
 import static java.nio.charset.StandardCharsets.UTF_8;
 import static java.util.Optional.empty;
 import static java.util.Optional.of;
+import static moe.yushi.authlibinjector.util.IOUtils.asBytes;
 import static moe.yushi.authlibinjector.util.IOUtils.asString;
-import static moe.yushi.authlibinjector.util.IOUtils.getURL;
 import static moe.yushi.authlibinjector.util.IOUtils.removeNewLines;
 import java.io.IOException;
 import java.io.UncheckedIOException;
 import java.lang.instrument.ClassFileTransformer;
+import java.net.HttpURLConnection;
+import java.net.MalformedURLException;
+import java.net.URL;
+import java.net.URLConnection;
 import java.util.Base64;
 import java.util.Optional;
 import java.util.concurrent.atomic.AtomicBoolean;
@@ -61,8 +65,18 @@ public final class AuthlibInjector {
 	 */
 	public static final String PROP_DUMP_CLASS = "authlibinjector.dumpClass";
 
+	/**
+	 * The side that authlib-injector runs on.
+	 * Possible values: client, server.
+	 */
+	public static final String PROP_SIDE = "authlibinjector.side";
+
+	public static final String PROP_ALI_REDIRECT_LIMIT = "authlibinjector.ali.redirectLimit";
+
 	// ====
 
+	private static final int REDIRECT_LIMIT = Integer.getInteger(PROP_ALI_REDIRECT_LIMIT, 5);
+
 	private AuthlibInjector() {}
 
 	private static AtomicBoolean booted = new AtomicBoolean(false);
@@ -99,7 +113,10 @@ public final class AuthlibInjector {
 		String apiRoot = System.getProperty(PROP_API_ROOT);
 		if (apiRoot == null) return empty();
 
-		apiRoot = appendSuffixSlash(apiRoot);
+		ExecutionEnvironment side = detectSide();
+		Logging.LAUNCH.fine("Detected side: " + side);
+
+		apiRoot = parseInputUrl(apiRoot);
 		Logging.CONFIG.info("API root: " + apiRoot);
 		warnIfHttp(apiRoot);
 
@@ -107,8 +124,40 @@ public final class AuthlibInjector {
 
 		Optional<String> prefetched = getPrefetchedResponse();
 		if (!prefetched.isPresent()) {
+
 			try {
-				metadataResponse = asString(getURL(apiRoot));
+				HttpURLConnection connection;
+				boolean redirectAllowed = side == ExecutionEnvironment.SERVER;
+				int redirectCount = 0;
+				for (;;) {
+					connection = (HttpURLConnection) new URL(apiRoot).openConnection();
+					Optional<String> ali = getApiLocationIndication(connection);
+					if (ali.isPresent()) {
+						if (!redirectAllowed) {
+							Logging.CONFIG.warning("Redirect is not allowed, ignoring ALI: " + ali.get());
+							break;
+						}
+
+						connection.disconnect();
+
+						apiRoot = ali.get();
+						if (redirectCount >= REDIRECT_LIMIT) {
+							Logging.CONFIG.severe("Exceeded maximum number of redirects (" + REDIRECT_LIMIT + "), refusing to redirect to: " + apiRoot);
+							throw new InjectorInitializationException();
+						}
+						redirectCount++;
+						Logging.CONFIG.info("Redirect to: " + apiRoot);
+						warnIfHttp(apiRoot);
+					} else {
+						break;
+					}
+				}
+
+				try {
+					metadataResponse = asString(asBytes(connection.getInputStream()));
+				} finally {
+					connection.disconnect();
+				}
 			} catch (IOException e) {
 				Logging.CONFIG.severe("Failed to fetch metadata: " + e);
 				throw new InjectorInitializationException(e);
@@ -155,6 +204,60 @@ public final class AuthlibInjector {
 		}
 	}
 
+	private static String parseInputUrl(String url) {
+		String lowercased = url.toLowerCase();
+		if (!lowercased.startsWith("http://") && !lowercased.startsWith("https://")) {
+			url = "https://" + url;
+		}
+
+		url = appendSuffixSlash(url);
+		return url;
+	}
+
+	private static Optional<String> getApiLocationIndication(URLConnection conn) {
+		return Optional.ofNullable(conn.getHeaderFields().get("X-Authlib-Injector-API-Location"))
+				.flatMap(list -> list.isEmpty() ? Optional.empty() : Optional.of(list.get(0)))
+				.flatMap(indication -> {
+					String currentUrl = appendSuffixSlash(conn.getURL().toString());
+					String newUrl;
+					try {
+						newUrl = appendSuffixSlash(new URL(conn.getURL(), indication).toString());
+					} catch (MalformedURLException e) {
+						Logging.CONFIG.warning("Failed to resolve absolute ALI, the header is [" + indication + "]. Ignore it.");
+						return Optional.empty();
+					}
+
+					if (newUrl.equals(currentUrl)) {
+						return Optional.empty();
+					} else {
+						return Optional.of(newUrl);
+					}
+				});
+	}
+
+	private static ExecutionEnvironment detectSide() {
+		String specifiedSide = System.getProperty(PROP_SIDE);
+		if (specifiedSide != null) {
+			switch (specifiedSide) {
+				case "client":
+					return ExecutionEnvironment.CLIENT;
+				case "server":
+					return ExecutionEnvironment.SERVER;
+				default:
+					Logging.LAUNCH.warning("Invalid value [" + specifiedSide + "] for parameter " + PROP_SIDE + ", ignoring.");
+					break;
+			}
+		}
+
+		// fallback
+		if (System.getProperty(PROP_PREFETCHED_DATA) != null || System.getProperty(PROP_PREFETCHED_DATA_OLD) != null) {
+			Logging.LAUNCH.warning("Prefetched configuration must be used along with parameter " + PROP_SIDE);
+			return ExecutionEnvironment.CLIENT;
+		} else {
+			return ExecutionEnvironment.SERVER;
+		}
+	}
+
 	private static ClassTransformer createTransformer(YggdrasilConfiguration config) {
 		ClassTransformer transformer = new ClassTransformer();
 		transformer.debugSaveClass = "true".equals(System.getProperty(PROP_DUMP_CLASS));
diff --git a/src/main/java/moe/yushi/authlibinjector/ExecutionEnvironment.java b/src/main/java/moe/yushi/authlibinjector/ExecutionEnvironment.java
new file mode 100644
index 0000000..a1a11b8
--- /dev/null
+++ b/src/main/java/moe/yushi/authlibinjector/ExecutionEnvironment.java
@@ -0,0 +1,5 @@
+package moe.yushi.authlibinjector;
+
+public enum ExecutionEnvironment {
+	CLIENT, SERVER;
+}