update connecting to mention S3 when needed

Author: bentsku

src/content/docs/aws/connecting/aws-cli.md

@@ -45,7 +45,8 @@ aws --endpoint-url=http://localhost.localstack.cloud:4566 kinesis list-streams
 
 :::note
 
-To enable the creation of pre-signed URLs for S3 buckets, please set both `AWS_ACCESS_KEY_ID` and `AWS_SECRET_ACCESS_KEY` to the value "test." Our pre-signed URL signature verification algorithm validates the pre-signed URL and its expiration.
+Pre-signed URLs for S3 are generated with the credentials configured on the client, such as the default `test`/`test` pair shown above.
+For LocalStack to be able to validate a pre-signed URL, it must be generated with valid credentials. More details at [S3 signature validation](/aws/services/s3/#signature-validation).
 :::
 
 ### Configuring a custom profile

src/content/docs/aws/connecting/credentials.md

@@ -41,6 +41,8 @@ In all such cases, the account ID is evaluated to `000000000000`.
 
 ## Secret Access Key
 
-The value of the secret access key are currently ignored by LocalStack.
+The value of the secret access key is generally ignored by LocalStack.
+We recommend using the same value as access key ID or `test`.
 
-We recommend using the same value as access key ID or `test`
+S3 can optionally validate request signatures, in which case the secret access key matters: it must be the secret the access key ID was issued with, or `test` for access key IDs not issued by LocalStack.
+See [S3 signature validation](/aws/services/s3/#signature-validation) for details.