Triage: we should correct the default here, and also make the message customizable since users can modify the set of allowed characters in the username.

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We're moving this issue to the .NET 7 Planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
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Thanks for contacting us.

We're moving this issue to the .NET 8 Planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues.
To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.

Thanks for contacting us.

We're moving this issue to the .NET 8 Planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues.
To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.

I just typed in an example from a Adam Freeman's book, where .AllowedUserNameCharacters are set to lowercase letters a-z only.
The default error message "... can only contain letters or digits" is definitely misleading, since no digits allowed. That would drive possible users crazy. (OK, granted, a site that only allows lowercase letters for user names probably needs to think about usability as well...)
Nevertheless, when customizing the usable alphabet is possible, then customizing the error message should be as well, allowing to refer to the special rules. Or is it already changeable?

i got this error: Username is invalid, can only contain letters or digits.
if i add the user name field in registration and try to use user name like this: test user
but if i use: testuser
i do not see the error and found out that we cannot have space between the user name because it treating UserName as email also.
If any one know how to fix this provide the solution.

I wouldn't mind having a look at this in the new year, however, I would like to hear from the ASP.NET Core team what kind of solution they'd like.

• Do we need to change the current default sentence?
• Does the message need to become customizable, somehow?
• Or would it need to change automatically based on the AllowedUserNameCharacters?