
legitimieren
to legitimize
To recognize or declare something as lawful or justified; to create a legal or moral basis for something.
Die Wahl hat die neue Regierung legitimiert.
The election legitimized the new government.
to legitimize / to identify oneself
Loading your saved state.

to legitimize
To recognize or declare something as lawful or justified; to create a legal or moral basis for something.
Die Wahl hat die neue Regierung legitimiert.
The election legitimized the new government.

to identify oneself
To prove one's own identity or authorization, typically by showing an ID card or another official document.
Alle Besucher müssen sich am Empfang mit einem Personalausweis legitimieren.
All visitors must identify themselves at reception with an ID card.
'Legitimieren' (to legitimize) is derived from the adjective 'legitim' (legitimate, lawful, justified). So the verb means to recognize something as legitimate or to prove one's own legitimacy.
Durch seine guten Argumente konnte er seine Position legitimieren.
With his good arguments, he was able to legitimize his position.
When it is about proving one's own identity, the verb is always used reflexively: 'sich legitimieren' (to identify oneself). The subject and the reflexive pronoun are the same person.
Können Sie sich bitte mit einem gültigen Dokument legitimieren?
Could you please identify yourself with a valid document?
When proving identity, the preposition 'mit' (with) and the dative are often used to name the document. Typical patterns are 'sich mit einem Ausweis/Pass legitimieren' (to identify oneself with an ID card/passport).
Am Eingang musste ich mich mit meinem Presseausweis legitimieren.
At the entrance, I had to identify myself with my press ID.
In the meaning 'rechtfertigen' (to justify), 'legitimieren' (to legitimize) is often used with abstract objects in the accusative. Common combinations are to legitimize 'eine Handlung' (an action), 'eine Entscheidung' (a decision), or 'eine Machtposition' (a position of power).
Der König versuchte, seinen Anspruch auf den Thron zu legitimieren.
The king tried to legitimize his claim to the throne.
to justify
Both words can be used in connection with a controversial decision. Rechtfertigen means giving good reasons and defending the decision as right or acceptable; legitimieren means recognizing that it is justified or creating such a basis for it. When the focus is on providing reasons, rechtfertigen is appropriate; when it is on establishing legitimacy, use legitimieren.

Die Zustimmung der Bürger kann die umstrittene Entscheidung legitimieren.
The citizens’ approval can legitimize the controversial decision.
Die Ministerin muss die umstrittene Entscheidung mit guten Gründen rechtfertigen.
The minister must justify the controversial decision with good reasons.