WebDAV 5.21 authentication error "could not handle non-ASCII username in Digest challenge"

I use WinSCP to connect via WebDAV to my employer's store on the BigCommerce ecommerce platform.

Starting with v. 5.21, when I try to connect, I receive the authentication error message,

Could not authenticate to server: could not handle non-ASCII username in Digest challenge / Connection failed

I rolled back to v. 5.19.6 and I'm able to authenticate without any problems.

I've attached my log file. I've replaced some sensitive data (store URL, username, etc.) with UPPERCASE GENERIC TEXT.

Additional info:

• Microsoft Windows 10 Pro v. 10.0.19044 Build 19044
  
• GUI w/Explorer interface
  

We are BigCommerce customer -
To the letter, experience the same issue and receive the same error messaging as the OP.
Attached log file following the same methodology specified by OP.

Edition: Windows 10 Enterprise
Version: 21H2
OS build: 19044.1706
Experience: Windows Feature Experience Pack 120.2212.4170.0
GUI: Explorer Interface

Thanks for your reports. Please post logs from 5.19.6 for comparison.

Absolutely. See attached.

A few items have been replaced by UPPERCASE TEXT for security. If I've deleted anything important to your analysis, let me know.

So does your username really contain non-ASCII characters? Were your given that username? Or did you chose it?

My username is my email address. It contains only ASCII characters in the original 128-character set, including @ (ASCII #64) and . (ASCII #46).

@MrWhipple: Thanks for your response.

Can you send me an email, so I can send you back a development version of WinSCP for testing? Please include a link back to this topic in your email. Also note in this topic that you have sent the email. Thanks.

Email sent. Thanks!

I have this same problem and have also reverted back to 5.19.6.
5.21.1 has this same problem. I tried it, got the same error, reverted back to 5.19.6

I have added this issue to the tracker:
Issue 2095 – Cannot authenticate to WebDAV server with username containing some special characters

I am also a Big Commerce user and have just downloaded WinSCP and am receiving the same error message when I try to login with my details. Any assistance would be gratefully received!

@glyn.andrews: Just upgrade to the latest version of WinSCP.