refactor(session_secret): use existing randomSecureToken function

[pano9000]

Hi,

this PR repalces the randomValueHex function (which is not used anywhere else across the codebase) with the already existing randomSecureToken function from the utils module for the creation of the session.

They both are using the randomBytes method of the crypto module.

This also improves secret security, as randomSecureToken uses Base64 and hence a much larger charset size than randomValueHex (which also unnecessarily was made even a bit more insecure, by having all characters UPPERCASED, so an even smaller charset size).

Some examples:

$ for i in $(<hashB64.txt); do echo "$i | $(echo $i | ent | head -1)"; done

XkPHvfhZISIS0OsfO6TzRbQkSdnTNLUZ0r+1qu9TD0CEm17isJ21tYUY5QjD/q7P | Entropy = 5.329759 bits per byte.
dGPMvn95YlRKOca65WMG+BgnMr94rl9Rh5Ac2gZQwBUrvrgJ+LGkoZ3UyghVFSfU | Entropy = 5.133530 bits per byte.
QkPieq6Q7zWnWddgSDEZFV6tVvGEBvQqMRlRbfbxCJUbh9tf47tRtzZCEjuS0oly | Entropy = 5.206682 bits per byte.
Bt0mAtgzbB4gcFbxdvjx/5d5/4fujhKLZKNweP3VkgdTLZCWoY90L17gLOAI3G6M | Entropy = 5.303062 bits per byte.
4J6mddl3QCn96aWzfhXaTGLQxF3WRHUihABGUl+Hng8FvsK8NBN9uO2V0UiMkrtC | Entropy = 5.395370 bits per byte.
JSsRWnyqix/zIDHbWBpqeCzv/Gm0FmWYXzzkI6Yl8nRMhcLc+c4F5AUs4s/zJmTr | Entropy = 5.231844 bits per byte.
LE66pEBu4HvGO+k9Z5oEf6dzj79tkA0D6A+iuuGcugjwjfnOWU0gojxfb39zILd6 | Entropy = 5.039686 bits per byte.
ymEHUcjsBqAQY8Tcpm3QYBABSUqsSlPXQTifwIQRjigj1Modi7RN7ryEpLUkoUJX | Entropy = 5.095219 bits per byte.
c/AQHlm75lMG9/aGCgdy0YsNclS2LG97PDpnibOqjjK4vDVpHT74betFrjvpUhNq | Entropy = 5.348915 bits per byte.
CDQRfJMYPS2JfX0+ebOW9wAIN2v0REHmRzNAXNrVx53lbzo3g+puXJSO4nf8x+ju | Entropy = 5.275763 bits per byte.

vs previously used secrets

DA00B0B76F686C86BD8C3F5F14E7649C7F05A3B00E724C011A889AD04491F62B | Entropy = 3.938397 bits per byte.
DCEB458061F12442558E5D753E64050F2FEEA31F8C505A23DEEA05E820186B6C | Entropy = 3.802707 bits per byte.
BB22E1348C91304C455952221EF5D03A79FCEBDF062283A9CBDDD1ED7D447541 | Entropy = 3.925496 bits per byte.
B3B12C0FE42981C4D4FBFEA53C59C042D4BB2B41935877BC36D2025FB57E8B39 | Entropy = 3.885335 bits per byte.
04A8B12F33D2C54C39CBA3E0C740BA06B05127AD945D945F9DFB185F8D848356 | Entropy = 3.951944 bits per byte.
D8482D98FF959A3513C9B7A20B2673C1559C1177405C5A907F3F604455E0B525 | Entropy = 3.896014 bits per byte.
BB8E2F63499F5784E17CC917067D9853C4F79FB8702FE2D2857E871FF66633B3 | Entropy = 3.852987 bits per byte.
47935A3736BB22CC1DB5BF439A571759A4579F5C35AF798CCE7267D28645C544 | Entropy = 3.771938 bits per byte.
5130CD305A37ABE22885C52020653DF08CC3D23A0752EC95C0D54FEC1D5E1ADF | Entropy = 3.766579 bits per byte.
94FAFB0A15E7012B67907EBDFABCB3817495AEF7FDA10DF6615C1128E818A650 | Entropy = 3.909164 bits per byte.

This will only affect newly created newly created session secrets only.