1 files changed, 54 insertions, 0 deletions
diff --git a/src/main/java/moe/nea/prickly/util/OAuthUtil.java b/src/main/java/moe/nea/prickly/util/OAuthUtil.java
new file mode 100644
index 0000000..ec3b7fd
--- /dev/null
+++ b/src/main/java/moe/nea/prickly/util/OAuthUtil.java
@@ -0,0 +1,54 @@
+/* (C) 2025 Linnea Gräf - Licensed to everyone under the BSD 3 Clause License */
+package moe.nea.prickly.util;
+
+import com.google.common.base.Preconditions;
+import com.google.common.base.Splitter;
+import java.net.URI;
+import java.util.List;
+import java.util.Objects;
+import org.jspecify.annotations.Nullable;
+
+public class OAuthUtil {
+	private static final Splitter SCOPE_SPLITTER =
+			Splitter.on(' ').omitEmptyStrings().trimResults();
+
+	public static List<String> parseScopes(@Nullable String scope) {
+		if (scope == null) return List.of();
+		return SCOPE_SPLITTER.splitToList(scope);
+	}
+
+	public static URI verifyRedirectUrl(@Nullable String actualRedirectUri, String expectedRedirectUri) {
+		Objects.requireNonNull(expectedRedirectUri, "expected redirect uri is null");
+		if (actualRedirectUri == null) return verifyRedirectUrl(expectedRedirectUri, expectedRedirectUri);
+
+		var expected = URI.create(expectedRedirectUri);
+		var actual = URI.create(actualRedirectUri).normalize();
+		Preconditions.checkArgument(actual.isAbsolute(), "redirect URI must be absolute");
+		Preconditions.checkArgument(actual.getFragment() == null, "redirect URI must not have a fragment");
+		Preconditions.checkArgument(
+				Objects.equals(actual.getScheme(), expected.getScheme()),
+				"scheme differs from registered redirect URI");
+		Preconditions.checkArgument(
+				Objects.equals(actual.getAuthority(), expected.getAuthority()),
+				"origin differs from registered redirect URI");
+		Preconditions.checkArgument(actual.getUserInfo() == null, "redirect URI must not have a user info");
+		Preconditions.checkArgument(
+				expected.getPath() == null || actual.getPath().startsWith(expected.getPath()),
+				"redirect URI must be a subpath of registered redirect URI");
+		return actual;
+	}
+
+	public static ResponseType parseResponseType(@Nullable String responseType) {
+		return switch (responseType) {
+			case "code" -> ResponseType.CODE;
+			case "token" -> ResponseType.TOKEN;
+			case null -> throw new IllegalArgumentException("missing response_type");
+			default -> throw new IllegalArgumentException("invalid response_type " + responseType);
+		};
+	}
+
+	public enum ResponseType {
+		TOKEN,
+		CODE
+	}
+}