** Okta's OKTA.O shares up 4.3% premarket to $109.28 as digital identity management co set to join S&P MidCap 400 index .IDX this week

** OKTA shares on course to rise for sixth straight session, if gains hold

** OKTA to replace Berry Global BERY.N in the IDX effective Thurs, May 1, the S&P Dow Jones Indices said late Mon

** Switzerland-based Amcor Plc AMCR.N to acquire U.S. packaging peer Berry in $8.4 bln deal

** In an index rebalancing note, Stephens said it expects passive funds will need to purchase 18.4 mln OKTA shares, which is about 6 days of buying demand, based on stock's 3-mth avg daily trading volume of 3.3 mln shares

** Over the last five years, stocks of new IDX adds outperformed on avg by 6.1% on the day after the index inclusion announcement, and by 5.6% between announcement and add, Stephens said

** With ~173.6 mln shares outstanding, OKTA has ~$18.2 bln market value - LSEG data

** Through Mon close, stock up 33% YTD

** Of 44 analysts covering OKTA, recommendation breakdown is 26 "strong buy" or "buy", 17 "hold" and 1 "sell"; median PT of $120 up from $105 on Feb 28

(Lance Tupper is a Reuters market analyst. The views expressed are his own)

((lance.tupper@tr.com 1-646-279-6380))