Add env test

src/main/java/com/imgfloat/app/config/TwitchCredentialsValidator.java

@@ -0,0 +1,31 @@
+package com.imgfloat.app.config;
+
+import jakarta.annotation.PostConstruct;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.stereotype.Component;
+import org.springframework.util.StringUtils;
+
+@Component
+public class TwitchCredentialsValidator {
+    private final String clientId;
+    private final String clientSecret;
+
+    public TwitchCredentialsValidator(
+            @Value("${spring.security.oauth2.client.registration.twitch.client-id}") String clientId,
+            @Value("${spring.security.oauth2.client.registration.twitch.client-secret}") String clientSecret) {
+        this.clientId = clientId;
+        this.clientSecret = clientSecret;
+    }
+
+    @PostConstruct
+    void validate() {
+        ensurePresent(clientId, "TWITCH_CLIENT_ID");
+        ensurePresent(clientSecret, "TWITCH_CLIENT_SECRET");
+    }
+
+    private void ensurePresent(String value, String name) {
+        if (!StringUtils.hasText(value) || "changeme".equalsIgnoreCase(value.trim())) {
+            throw new IllegalStateException(name + " must be set in the environment or .env file");
+        }
+    }
+}