Just putting this out here, have fun

common/src/main/java/eu/midnightdust/selectiveauth/SelectiveAuth.java

@@ -0,0 +1,11 @@
+package eu.midnightdust.selectiveauth;
+
+import eu.midnightdust.selectiveauth.config.SelectiveAuthConfig;
+
+public class SelectiveAuth {
+    public static final String MOD_ID = "selectiveauth";
+
+    public static void init() {
+        SelectiveAuthConfig.init(MOD_ID, SelectiveAuthConfig.class);
+    }
+}

common/src/main/java/eu/midnightdust/selectiveauth/config/SelectiveAuthConfig.java

@@ -0,0 +1,10 @@
+package eu.midnightdust.selectiveauth.config;
+
+import com.google.common.collect.Lists;
+import eu.midnightdust.lib.config.MidnightConfig;
+
+import java.util.List;
+
+public class SelectiveAuthConfig extends MidnightConfig {
+    @Entry public static List<String> authlessPlayers = Lists.newArrayList();
+}

common/src/main/java/eu/midnightdust/selectiveauth/mixin/MixinServerLoginNetworkHandler.java

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+package eu.midnightdust.selectiveauth.mixin;
+
+import com.llamalad7.mixinextras.injector.ModifyExpressionValue;
+import eu.midnightdust.selectiveauth.config.SelectiveAuthConfig;
+import net.minecraft.server.network.ServerLoginNetworkHandler;
+import org.jetbrains.annotations.Nullable;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+
+@Mixin(ServerLoginNetworkHandler.class)
+public class MixinServerLoginNetworkHandler {
+    @Shadow @Nullable String profileName;
+
+    @ModifyExpressionValue(
+            method = "onHello",
+            at = @At(value = "INVOKE", target = "Lnet/minecraft/server/MinecraftServer;isOnlineMode()Z")
+    )
+    private boolean selectiveauth$skipAuthForSelectedPlayers(boolean isOnlineMode) {
+        return isOnlineMode && !SelectiveAuthConfig.authlessPlayers.contains(this.profileName);
+    }
+}

common/src/main/resources/selectiveauth.mixins.json

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+{
+  "required": true,
+  "minVersion": "0.8",
+  "package": "eu.midnightdust.selectiveauth.mixin",
+  "compatibilityLevel": "JAVA_17",
+  "mixins": [
+    "MixinServerLoginNetworkHandler"
+  ],
+  "injectors": {
+    "defaultRequire": 1
+  }
+}