BE: Auth: impl opaque token auth

[germanosin]

• Breaking change? (if so, please describe the impact and migration path for existing application instances)

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How Has This Been Tested? (put an "x" (case-sensitive!) next to an item)

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• I have performed a self-review of my own code
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• I have made corresponding changes to the documentation (e.g. ENVIRONMENT VARIABLES)
• My changes generate no new warnings (e.g. Sonar is happy)
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged

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[germanosin]

Related to #659