POST em /oauth/token com clientid, clientsecret e certificado.
Aí ele vem na resposta:
{
"access_token": "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c",
"token_type": "Bearer",
"expires_in": 3600,
"scope": "cob.read cob.write pix.read pix.write"
}