…#504)

(cherry picked from commit d49b9f0)

The secrets module should be used for generating cryptographically
strong random numbers suitable for managing data such as passwords,
account authentication, security tokens, and related secrets.

In particularly, secrets should be used in preference to the default
pseudo-random number generator in the random module, which is
designed for modelling and simulation, not security or cryptography.

(cherry picked from commit d21fd53)

Fixed some copy and paste typos, see issue oauthlib#532.

(cherry picked from commit 1b3498a)

(cherry picked from commit 657065d)

(cherry picked from commit 0b6f7e2)