diff --git a/docs/services/sda.md b/docs/services/sda.md
index ecae4e1..9affbc0 100644
--- a/docs/services/sda.md
+++ b/docs/services/sda.md
@@ -17,8 +17,9 @@ The SDA submission pipeline has four main steps:
 
 There are also additional support services:
 
-1. [Intercept](intercept.md) relays messages from `CentralEGA` to the system.
-2. [ReEncrypt](reencrypt.md) reencrypts a given file header with a given public key.
-3. [s3inbox](s3inbox.md) proxies uploads to the an S3 compatible storage backend.
-4. [sync](sync.md) mirrors ingested data between sites in the [Bigpicture](https://bigpicture.eu/) project.
-5. [syncapi](syncapi.md) is used in the [Bigpicture](https://bigpicture.eu/) project for mirroring data between two installations of SDA.
+1. [Auth](auth.md) authentication service used in conjunction with the [s3inbox](s3inbox.md).
+2. [Intercept](intercept.md) relays messages from `CentralEGA` to the system.
+3. [ReEncrypt](reencrypt.md) reencrypts a given file header with a given public key.
+4. [s3inbox](s3inbox.md) proxies uploads to the an S3 compatible storage backend.
+5. [sync](sync.md) mirrors ingested data between sites in the [Bigpicture](https://bigpicture.eu/) project.
+6. [syncapi](syncapi.md) is used in the [Bigpicture](https://bigpicture.eu/) project for mirroring data between two installations of SDA.