code: function put_token(oidc_token) {
      return new Promise((resolve, reject) => {
          dbMgr
              .updateOne("oidc_token", {
                  _id: {
                      $eq: oidc_token._id
                  }
              }, {
                  $currentDate: {
                      expire_on: true
                  },
                  $set: oidc_token
              }, {upsert: true})
              .then((result) => {
                  if (result.modifiedCount === 1) {
                      return resolve(oidc_token._id);
                  } else {
                      return reject(new Error("No oidc_token recoreds inserted"));
                  }
              }, (err) => {
                  reject(err);
              });
      });
  }
docs: This function return a Promse which resolves after updating a token record
  in the persistent stor. (rejects on errors )
  
  @param  {[type]} oidc_token [description]
  @return {[type]}                       [description]