On Wikipedia Legato means: [...] the player makes a transition from note to note with no intervening silence. [...]
Source: https://en.wikipedia.org/wiki/Legato
On Wikipedia Portamento means: [...] is a pitch sliding from one note to another. [...]
Source: https://en.wikipedia.org/wiki/Portamento
It seem to me, that both, Legato and Portamento slide from one note to another. So what is the difference?