2643202 - Rest Adapter throws HTTP 401 Unauthorized in case Basic Authentication is used and there is a backslash "\" in the username

You are using Process Integration (PI) or Process Orchestration (PO) Rest Receiver adapter with Basic Authentication and there is a backslash "\" in the username (e.g. "domain\username").

When connecting to the target server, it used to work fine, however after an upgrade/update in the system, the same is returning HTTP 401.

Checking the Message Logs, something similar to this is visible:

10/21/2019 06:56:19.190 PM Information Calling server: POST https://<server>:<port>/....
10/21/2019 06:56:19.350 PM Information Server returned code: 401
10/21/2019 06:56:19.351 PM Error HTTP error occurred: Unauthorized
10/21/2019 06:56:19.351 PM Error MP: exception caught with cause com.sap.aii.adapter.rest.ejb.common.exception.HttpCallException: HTTP POST call to https://<server>:<port>/.... not successful. Unauthorized
10/21/2019 06:56:19.376 PM Error Exception caught by adapter framework: HTTP POST call to https://<server>:<port>/.... not successful. Unauthorized

• SAP NetWeaver 7.5

Rest, Adapter, 401, Patch, Upgrade, Update, Authentication, Message, Failed, HTTP, Unauthorized, NTLM, Basic, Process Integration, PI, PO, Process Orchestration 7.5, PI 7.5, PO 7.5, XI, AEX , KBA , BC-XI-CON-RST , Rest Adapter , Problem