Don't auth if there is an existing bearer token

[markpeek]

The sdk client was requesting a new bearer token for each api call. This change will look for and use an existing bearer token prior to going through the authorization.

[vmwclabot]

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• Commit b442d4b must be signed by [email protected]

[Prativa20]

We should check the token expiry timestamp as well, so that we don't use the existing token that is expired.