Default OPA policies

[lazyniv]

Implementation of default OPA policies from #201

Depends on #225

Content:

• opautils package:
  • OPA input (see Prepare input for OPA #225 and Generalize authorize chain element #200 for more information)
  • OPA evaluation module -- to get policy decisions
• Default OPA policies examples (see Default Policy examples #201 for more information)
  • Tokens valid
  • No Tokens in path expired
  • Last Token matches TLSInfo
  • Token.Aud for token n in path matches Token.Sub for n+1 token in chain
• Use cases:
  • The case when we check that the chain is valid -- path_segments[n-1].Token.aud == path_segments[n].Token.sub (see scheme in spec)
• Rewrite authorization chain element