POST /as/token.oauth2 HTTP/1.1
 Host: as.example.com
 Content-Type: application/x-www-form-urlencoded

 grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Atoken-exchange
 &audience=urn%3Aexample%3Acooperation-context
 &subject_token=eyJhbGciOiJFUzI1NiIsImtpZCI6IjE2In0.eyJhdWQiOiJodHRwc
   zovL2FzLmV4YW1wbGUuY29tIiwiaXNzIjoiaHR0cHM6Ly9vcmlnaW5hbC1pc3N1ZXI
   uZXhhbXBsZS5uZXQiLCJleHAiOjE0NDE5MTAwNjAsInNjb3BlIjoic3RhdHVzIGZlZ
   WQiLCJzdWIiOiJ1c2VyQGV4YW1wbGUubmV0IiwibWF5X2FjdCI6eyJzdWIiOiJhZG1
   pbkBleGFtcGxlLm5ldCJ9fQ.4rPRSWihQbpMIgAmAoqaJojAxj-p2X8_fAtAGTXrvM
   xU-eEZHnXqY0_AOZgLdxw5DyLzua8H_I10MCcckF-Q_g
 &subject_token_type=urn%3Aietf%3Aparams%3Aoauth%3Atoken-type%3Ajwt
 &actor_token=eyJhbGciOiJFUzI1NiIsImtpZCI6IjE2In0.eyJhdWQiOiJodHRwczo
   vL2FzLmV4YW1wbGUuY29tIiwiaXNzIjoiaHR0cHM6Ly9vcmlnaW5hbC1pc3N1ZXIuZ
   XhhbXBsZS5uZXQiLCJleHAiOjE0NDE5MTAwNjAsInN1YiI6ImFkbWluQGV4YW1wbGU
   ubmV0In0.7YQ-3zPfhUvzje5oqw8COCvN5uP6NsKik9CVV6cAOf4QKgM-tKfiOwcgZ
   oUuDL2tEs6tqPlcBlMjiSzEjm3yBg
 &actor_token_type=urn%3Aietf%3Aparams%3Aoauth%3Atoken-type%3Ajwt