a.3.- Sample authentication script (Linux)

#!/bin/bash
PRIVATE_KEY_ES256=$2
CLIENT_ID=$1
SCOPE="das-api/das-access"
ISSUER="https://logindev.wipo.int/am/oauth2"
 
# https://logindev.wipo.int/am/oauth2/.well-known/openid-configuration
OIDC_CONFIG_JSON=$(curl -k "${ISSUER}/.well-known/openid-configuration")
 
# Generic way to obtain the token endpoint
TOKEN_ENDPOINT=$(printf '%s' ${OIDC_CONFIG_JSON} | jq -r ".token_endpoint")
 
UTC_TIME=$(date -u +%s)
EXP_TIME=$(expr "$UTC_TIME" + 10)
 
JSON='{'
JSON=${JSON}$(printf '"iss":"%s"' ${CLIENT_ID})
JSON=${JSON}$(printf ',"sub":"%s"' ${CLIENT_ID})
JSON=${JSON}$(printf ',"aud":"%s"' ${TOKEN_ENDPOINT})
JSON=${JSON}$(printf ',"exp":%s' ${EXP_TIME})
JSON=${JSON}'}'
 
JSON_HEADER_B64=$(printf '{"alg":"ES256","typ":"JWT"}' | jq -cj | base64 -w0 | tr -d '\n=' | tr '+/' '-_')
JSON_PAYLOAD_B64=$(printf $JSON | jq -cj | base64 -w0 | tr -d '\n=' | tr '+/' '-_')
JSON_SIGNATURE_ASN1_B64=$(printf '%s.%s' $JSON_HEADER_B64 $JSON_PAYLOAD_B64 | openssl dgst -sha256 -sign "${PRIVATE_KEY_ES256}" | openssl asn1parse -inform DER | base64 -w0)
JSON_SIGNATURE_HEX=$(printf $JSON_SIGNATURE_ASN1_B64 | base64 -d | sed -n '/INTEGER/p' | sed 's/.*INTEGER\s*://g' | sed -z 's/[^0-9A-F]//g')
JSON_SIGNATURE_B64=$(printf $JSON_SIGNATURE_HEX | xxd -p -r | base64 -w0 | tr -d '\n=' | tr '+/' '-_')
 
JWT_ASSERTION=$(printf '%s.%s.%s' $JSON_HEADER_B64 $JSON_PAYLOAD_B64 $JSON_SIGNATURE_B64)
# echo $JWT_ASSERTION
 
# Access token private_key_jwt
curl --insecure \
  --header "Content-Type: application/x-www-form-urlencoded" \
  --data-urlencode "grant_type=client_credentials" \
  --data-urlencode scope="${SCOPE}" \
  --data-urlencode "client_assertion_type=urn:ietf:params:oauth:client-assertion-type:jwt-bearer" \
  --data-urlencode "client_assertion=${JWT_ASSERTION}" \
  --url "${TOKEN_ENDPOINT}"