The Artificer class, introduced in Unearthed Arcana, has a feature she gains at fourth level titled Infuse Magic. This feature allows the Artificer to implant a spell into an item for later use by anyone with an Intelligence ability score greater than 6. I'm unsure of whether the activated spell should use the Artificer's concentration or the users.
On one hand, using the artificer's concentration seems problematic. A player could unknowingly end the effects of an important spell on an ally by hijacking the artificer's concentration.
On the other hand, using the user's concentration means the artificer can have multiple helpful effects active at one time, something no other class can do. This may be the intended power level, but it could also be considered overpowered.
I know that Unearthed Arcana is playtest material and is not in a finished, polished state. This problem may be resolved in a future rework of the class.
What I'm looking for is an answer that specifies which character's concentration should be used for spellcasting from an imbued item, citing a definitive source, such as a statement by the designers, a rule I may have missed in the spellcasting rules, or something from the UA article itself.