Extract bearer token from Authorization when separated by multiple spaces

[#1]

How do you capture an OAuth access token into a variable when the token is separated from the Bearer authentication scheme keyword by multiple spaces?

The Authorization header has this ABNF:

credentials = auth-scheme [ 1*SP ( token68 / [ ( "," / auth-param )
    *( OWS "," [ OWS auth-param ] ) ] ) ]

RFC 6750 says that the auth-scheme in that ABNF is "bearer" (case insensitive), so I have to extract the token from the value after that with any amount of spaces.

I have found only one way to do this and it is very kludgey: Extract the token with preceding spaces and use a bit of JavaScript to trim it. So, this means I have an Extract like this:

<ExtractVariables name="Extract-Access-Token">
    <DisplayName>Extract access token from Authorization request header</DisplayName>
    <Header name="Authorization">
        <!-- No space between "Bearer" and the accessToken variable -->
        <Pattern ignoreCase="true">Bearer{accessToken}</Pattern>
    </Header>
    <IgnoreUnresolvedVariables>true</IgnoreUnresolvedVariables>
    <VariablePrefix>clientRequest</VariablePrefix>
</ExtractVariables>

Then, I can use a bit of JavaScript to trim the leading spaces. This is less than ideal. Is there no better way?

TIA!