# Equally spaced bibliography keys using biblatex

I'm working at a bibliography with biblatex. I have to format my cite keys to match some requirements. My current problem is that I found no option to change the horizontal spacing/alignment of the keys. That's my current setup:

I want it to have the keys spaced equally so that the brackets align like this (but only in the bibliography itself):

Text with citation [CD] and this [OBB]

Bibliography:
[  CD ] Some text
[ OBB ] Some text


The important aspect here is the alignment of the brackets. How can this be done? And further, is there a way to center the keys within the brackets?

\documentclass{scrartcl}

\usepackage[backend=biber,style=alphabetic,maxbibnames=1,maxcitenames=1,defernumbers,%
doi=false,isbn=false,clearlang=false,backref=false]{biblatex}
\DeclareFieldFormat{labelalpha}{\textsc{#1}}

\begin{filecontents}{bib.bib}
@ONLINE{text:source,
author={B. Obby},
title={Sources today},
url={http://www.example.com},
urldate={2017-02-20},}
@ONLINE{text:src,
author={Cicero, Marcus Tullius and Doe, John},
title={Sources tomorrow},
url={http://www.example.com},
urldate={2017-02-20},}
\end{filecontents}

\bibliography{bib}
\nocite{*}

\begin{document}

Text with citation and no extended spacing: \autocite{text:src}\\
Text witch citation and ordinary spacing: \autocite{text:source}

\printbibliography

\end{document}


\documentclass{scrartcl}

\usepackage[backend=biber,style=alphabetic,maxbibnames=1,maxcitenames=1,defernumbers,%
doi=false,isbn=false,clearlang=false,backref=false]{biblatex}
\DeclareFieldFormat{labelalpha}{\textsc{#1}}