Improve message about insecure S3 settings

modules/repository-s3/src/main/java/org/elasticsearch/repositories/s3/S3Repository.java

@@ -318,8 +318,7 @@ class S3Repository extends MeteredBlobStoreRepository {
             deprecationLogger.critical(
                 DeprecationCategory.SECURITY,
                 "s3_repository_secret_settings",
-                "Using s3 access/secret key from repository settings. Instead "
-                    + "store these in named clients and the elasticsearch keystore for secure settings."
+                INSECURE_CREDENTIALS_DEPRECATION_WARNING
             );
         }
 
@@ -336,6 +335,11 @@ class S3Repository extends MeteredBlobStoreRepository {
         );
     }
 
+    static final String INSECURE_CREDENTIALS_DEPRECATION_WARNING = Strings.format("""
+        This repository's settings include a S3 access key and secret key, but repository settings are stored in plaintext and must not be \
+        used for security-sensitive information. Instead, store all secure settings in the keystore. See [%s] for more information.\
+        """, ReferenceDocs.SECURE_SETTINGS);
+
     private static Map<String, String> buildLocation(RepositoryMetadata metadata) {
         return Map.of("base_path", BASE_PATH_SETTING.get(metadata.settings()), "bucket", BUCKET_SETTING.get(metadata.settings()));
     }

modules/repository-s3/src/test/java/org/elasticsearch/repositories/s3/RepositoryCredentialsTests.java

@@ -107,10 +107,9 @@ public void testRepositoryCredentialsOverrideSecureCredentials() {
         assertThat(credentials.getAWSSecretKey(), is("insecure_aws_secret"));
 
         assertCriticalWarnings(
+            "[access_key] setting was deprecated in Elasticsearch and will be removed in a future release.",
             "[secret_key] setting was deprecated in Elasticsearch and will be removed in a future release.",
-            "Using s3 access/secret key from repository settings. Instead store these in named clients and"
-                + " the elasticsearch keystore for secure settings.",
-            "[access_key] setting was deprecated in Elasticsearch and will be removed in a future release."
+            S3Repository.INSECURE_CREDENTIALS_DEPRECATION_WARNING
         );
     }
 
@@ -194,10 +193,9 @@ public void testReinitSecureCredentials() {
 
         if (hasInsecureSettings) {
             assertCriticalWarnings(
+                "[access_key] setting was deprecated in Elasticsearch and will be removed in a future release.",
                 "[secret_key] setting was deprecated in Elasticsearch and will be removed in a future release.",
-                "Using s3 access/secret key from repository settings. Instead store these in named clients and"
-                    + " the elasticsearch keystore for secure settings.",
-                "[access_key] setting was deprecated in Elasticsearch and will be removed in a future release."
+                S3Repository.INSECURE_CREDENTIALS_DEPRECATION_WARNING
             );
         }
     }
@@ -238,10 +236,7 @@ public void sendResponse(RestResponse response) {
             throw error.get();
         }
 
-        assertWarnings(
-            "Using s3 access/secret key from repository settings. Instead store these in named clients and"
-                + " the elasticsearch keystore for secure settings."
-        );
+        assertWarnings(S3Repository.INSECURE_CREDENTIALS_DEPRECATION_WARNING);
     }
 
     private void createRepository(final String name, final Settings repositorySettings) {

server/src/main/java/org/elasticsearch/common/ReferenceDocs.java

@@ -82,6 +82,7 @@ public enum ReferenceDocs {
     CIRCUIT_BREAKER_ERRORS,
     ALLOCATION_EXPLAIN_NO_COPIES,
     ALLOCATION_EXPLAIN_MAX_RETRY,
+    SECURE_SETTINGS,
     // this comment keeps the ';' on the next line so every entry above has a trailing ',' which makes the diff for adding new links cleaner
     ;
 

server/src/main/java/org/elasticsearch/common/settings/SecureSetting.java

@@ -185,9 +185,7 @@ private InsecureStringSetting(String name) {
         @Override
         public SecureString get(Settings settings) {
             if (ALLOW_INSECURE_SETTINGS == false && exists(settings)) {
-                throw new IllegalArgumentException(
-                    "Setting [" + name + "] is insecure, " + "but property [allow_insecure_settings] is not set"
-                );
+                throw new IllegalArgumentException("Setting [" + name + "] is insecure and no longer supported");
             }
             return super.get(settings);
         }

server/src/main/resources/org/elasticsearch/common/reference-docs-links.txt

@@ -44,3 +44,4 @@ FORMING_SINGLE_NODE_CLUSTERS                                    modules-discover
 CIRCUIT_BREAKER_ERRORS                                          circuit-breaker-errors.html
 ALLOCATION_EXPLAIN_NO_COPIES                                    cluster-allocation-explain.html#no-valid-shard-copy
 ALLOCATION_EXPLAIN_MAX_RETRY                                    cluster-allocation-explain.html#maximum-number-of-retries-exceeded
+SECURE_SETTINGS                                                 secure-settings.html