Calculate PR-AUC from these points: recall (0.2, precision 1.0), (0.5, 0.8), (0.9, 0.5).

{
  "points": [
    [
      0.2,
      1
    ],
    [
      0.5,
      0.8
    ],
    [
      0.9,
      0.5
    ]
  ]
}