docs(veterans): first pass @ veterans use case docs

docs/use-cases/veterans.md

@@ -0,0 +1,26 @@
+# Veterans
+
+Another use case for the Benefits application is for U.S. veterans - people who have served in the active military, naval, or air service, and who were discharged or released therefrom under conditions other than dishonorable. The Benefits application verifies the person's veteran status to confirm eligibility and allows those eligible to enroll their contactless payment card for their transit benefit.
+
+On the back-end, the app uses the Identity Gateway to connect to the [Veteran Confirmation API](https://developer.va.gov/explore/api/veteran-confirmation) to confirm veteran status. On the front-end, users must create or log into their Login.gov account to complete the eligibility verification process.
+
+## Process
+
+```mermaid
+sequenceDiagram
+    actor Rider
+    participant Benefits as Benefits app
+    participant IdG as Identity Gateway
+    participant VA as VA.gov Confirmation API
+    participant Littlepay
+
+    Rider->>Benefits: visits site
+    Benefits-->>IdG: identity proofing
+    IdG-->>VA: identity proofing
+    Rider->>VA: enters SSN and ID
+    VA-->>IdG: eligibility verification
+    IdG-->>Benefits: eligibility verification
+    Benefits-->>Littlepay: enrollment start
+    Rider->>Littlepay: enters payment card details
+    Littlepay-->>Benefits: enrollment complete
+```