Is there any reason why okhttp3.Credentials use ISO_8859_1 instead UTF-8?

I am using okhttp3.Credentials to get Base64 string in my current project. I spot an issue with cyrillic symbols I passed on server as Base64 string and eventually find out current implementation of okhttp3.Credentials uses ISO_8859_1.

Is there a thoughtful intent to go with ISO_8859_1 here instead of more universal UTF-8?

Update from answer:

From reference to spec

The original definition of this authentication scheme failed to
specify the character encoding scheme used to convert the user-pass
into an octet sequence. In practice, most implementations chose
either a locale-specific encoding such as ISO-8859-1 ([ISO-8859-1]),
or UTF-8 ([RFC3629]). For backwards compatibility reasons, this
specification continues to leave the default encoding undefined, as
long as it is compatible with US-ASCII (mapping any US-ASCII
character to a single octet matching the US-ASCII character code).



B.3. Why not simply switch the default encoding to UTF-8?

There are sites in use today that default to a local character
encoding scheme, such as ISO-8859-1 ([ISO-8859-1]), and expect user
agents to use that encoding. Authentication on these sites will stop
working if the user agent switches to a different encoding, such as
UTF-8.

Note that sites might even inspect the User-Agent header field
([RFC7231], Section 5.5.3) to decide which character encoding scheme
to expect from the client. Therefore, they might support UTF-8 for
some user agents, but default to something else for others. User
agents in the latter group will have to continue to do what they do
today until the majority of these servers have been upgraded to
always use UTF-8.

Discussion here https://github.com/square/okhttp/pull/3134

It's legacy and you can override with the optional param.