There actually is such a band…
https://www.sentinel-hub.com/faq/how-can-i-access-data-landsat-8-quality-assessment-band

@gmilcinski I couldn’t find in the dashboard when i tried creating new layer on the sentinel-hub dashboard. Attached are the screenshots

Try using Custom script editor directly. e.g. write in there:
return [decodeLs8Qa(BQA).cloud];

Thanks. It is working. To verify whether it is returning correct results i printed distinct values returned from decodeLs8Qa(BQA).cloud. So, i am getting 0 in all the cases. what does 0 signify here. Similarly in case of decodeLs8Qa(BQA).cloudConfidence, decodeLs8Qa(BQA).cloudShadowConfidence, decodeLs8Qa(BQA).cirrusConfidence] return all the values to be 1 . Does these values mean cloud doesn’t exist or cannot determine the pixel? Just FYI In the L8L1CWCSInput i have mentioned maxcc to be 0.05.

Please post URL of your request, hiding the last two blocks of instance ID, so that we check, what is wrong.

@gmilcinski It could be because my AOI was very small 1kmX1km. Once again i face the same problem will post the URL. Moreover, could you please explain the meaning of values what does 0 and 1 signify in each case. Does these values mean cloud doesn’t exist or cannot determine the pixel?

The meaning of values is explained in the documentation of the utility function decodeLs8Qa