Basic authentication does not support non-ascii characters in usernames

Summary

Copied from ACJIRA-513:
When I call REST API using basic authentication and the user has a non-ASCII character in their name, e.g. 'ä', the status 401 (Unauthorized) is returned. The name:password string is converted into a byte array using UTF8 before base-64 encoding. I also tried ASCII, but that is not supposed to work anyway.
Please note that JIRA user names can contain non-ASCII characters (e.g. umlauts) and a user with such a name can log in to JIRA using the web UI. rest/auth/1/session processes names with non-ASCII characters fine as well.

Steps to Reproduce

1. Step 1 - Create a user with non-ASCII character name like "łukasz"
2. Step 2 - Do rest call as the user. "curl -u łukasz:test http://localhost:8090/jira/rest/api/2/issue/TEST-2"

Expected Results

Issue json should be returned for the user.

Actual Results

HTTP/1.1 401 Unauthorized
Content-Encoding: gzip
Content-Type: text/html;charset=UTF-8
Date: Thu, 18 Feb 2016 10:53:23 GMT
Server: Apache-Coyote/1.1
Set-Cookie: JSESSIONID=91304E14DAA60D5A14292013A062A13B; Path=/jira/; HttpOnly
Transfer-Encoding: chunked
Vary: User-Agent
WWW-Authenticate: OAuth realm="http%3A%2F%2Flocalhost%3A8090%2Fjira"
X-AREQUESTID: 1313x7361x1
X-ASEN: SEN
X-Content-Type-Options: nosniff
X-Seraph-LoginReason: AUTHENTICATED_FAILED

Notes

See ACJIRA-513 description and comments for more details.

Workaround

Remove non-ascii character from user name