Parse JWK in GO (Golang)

parse_jwk.go

package auth

import (
	"crypto/rsa"
	"encoding/base64"
	"encoding/json"
	"fmt"
	"math/big"
)

// https://login.microsoftonline.com/common/discovery/v2.0/keys

type JwkKey struct {
	KID  string `json:"kid"`
	Type string `json:"kty"`
	N    string `json:"n"`
	E    string `json:"e"`
}

type JwkKeys struct {
	Keys []JwkKey `json:"keys"`
}

type JwkRsaKey struct {
	KID    string
	PubKey *rsa.PublicKey
}

const SOURCE = `
{
  "keys": [
    {
      "kty": "RSA",
      "use": "sig",
      "kid": "u4OfNFPHwEBosHjtrauObV84LnY",
      "x5t": "u4OfNFPHwEBosHjtrauObV84LnY",
      "n": "oRRQG-ib30x09eWtDpL0wWahA-hgjc0lWoQU4lwBFjXV2PfPImiAvwxOxNG34Mgnw3K9huBYLsrvOQAbMdBmE8lwz8DFKMWqHqoH3xSqDGhIYFobQDiVRkkecpberH5hqJauSD7PiwDBSQ_RCDIjb0SOmSTpZR97Ws4k1z9158VRf4BUbGjzVt4tUAz_y2cI5JsXQfcgAPB3voP8eunxGwZ_iM8evw3hUOw7-nuiPyts7HSkvV6GMwrXfOymY_w07mYxw_2LnKInfsWBtcRIDG-Nrsj237LgtBhK7TkzuVrguq__-bkDwwF3qTRXGAX9KrwY4huRxDRslMIg30Hqgw",
      "e": "AQAB",
      "x5c": [
        "MIIDBTCCAe2gAwIBAgIQdEMOjSqDVbdN3mzb2IumCzANBgkqhkiG9w0BAQsFADAtMSswKQYDVQQDEyJhY2NvdW50cy5hY2Nlc3Njb250cm9sLndpbmRvd3MubmV0MB4XDTE5MDYwNDAwMDAwMFoXDTIxMDYwNDAwMDAwMFowLTErMCkGA1UEAxMiYWNjb3VudHMuYWNjZXNzY29udHJvbC53aW5kb3dzLm5ldDCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAKEUUBvom99MdPXlrQ6S9MFmoQPoYI3NJVqEFOJcARY11dj3zyJogL8MTsTRt+DIJ8NyvYbgWC7K7zkAGzHQZhPJcM/AxSjFqh6qB98UqgxoSGBaG0A4lUZJHnKW3qx+YaiWrkg+z4sAwUkP0QgyI29Ejpkk6WUfe1rOJNc/defFUX+AVGxo81beLVAM/8tnCOSbF0H3IADwd76D/Hrp8RsGf4jPHr8N4VDsO/p7oj8rbOx0pL1ehjMK13zspmP8NO5mMcP9i5yiJ37FgbXESAxvja7I9t+y4LQYSu05M7la4Lqv//m5A8MBd6k0VxgF/Sq8GOIbkcQ0bJTCIN9B6oMCAwEAAaMhMB8wHQYDVR0OBBYEFNRP0Lf6MDeL11RDH0uL7H+/JqtLMA0GCSqGSIb3DQEBCwUAA4IBAQCJKR1nxp9Ij/yisCmDG7bdN1yHj/2HdVvyLfCCyReRfkB3cnTZVaIOBy5occGkdmsYJ+q8uqczkoCMAz3gvvq1c0msKEiNpqWNeU2aRXqyL3QZJ/GBmUK1I0tINPVv8j7znm0DcvHHXFvhzS8E4s8ai8vQkcpyac/7Z4PN43HtjDnkZo9Zxm7JahHshrhA8sSPvsuC4dQAcHbOrLbHG+HIo3Tq2pNl7mfQ9fVJ2FxbqlzPYr/rK8H2GTA6N55SuP3KTNvyL3RnMa3hXmGTdG1dpMFzD/IE623h/BqY6j29PyQC/+MUD4UCZ6KW9oIzpi27pKQagH1i1jpBU/ceH6AW"
      ],
      "issuer": "https://login.microsoftonline.com/{tenantid}/v2.0"
    },
    {
      "kty": "RSA",
      "use": "sig",
      "kid": "ie_qWCXhXxt1zIEsu4c7acQVGn4",
      "x5t": "ie_qWCXhXxt1zIEsu4c7acQVGn4",
      "n": "68tx2cnOfkvHf705c-ZIZfXiyxE6c9LqxVQDjIs-9DbvDEI7453kZi9tvQYzskJFdBlD8MYuVhX8Bpi_YUFF8eoJ1PFC2_82sDhF-mNJ7sPrYsgMJAL3rfzOKQapx3m9RPS-18KAZOg-SIDwbNcrDm5rYw5oXi2jbO4ctKzRKP3jznvHDeLnLCTcnDGkMCRBuENJugwh7oHjtGph1L3vNpI2lroB3HK2TcD1Mr5cYTcrd-j6bmk8LRewLCJjipZwmu3DiW4_kRnigw8O5BmYgMYkWZ7Gl048KBZL-7PyHTAXb7tMp9FdJfWY-Xu9KB9ayAW84GbCMJ7qoojwoCDb3Q",
      "e": "AQAB",
      "x5c": [
        "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"
      ],
      "issuer": "https://login.microsoftonline.com/{tenantid}/v2.0"
    },
    {
      "kty": "RSA",
      "use": "sig",
      "kid": "M6pX7RHoraLsprfJeRCjSxuURhc",
      "x5t": "M6pX7RHoraLsprfJeRCjSxuURhc",
      "n": "xHScZMPo8FifoDcrgncWQ7mGJtiKhrsho0-uFPXg-OdnRKYudTD7-Bq1MDjcqWRf3IfDVjFJixQS61M7wm9wALDj--lLuJJ9jDUAWTA3xWvQLbiBM-gqU0sj4mc2lWm6nPfqlyYeWtQcSC0sYkLlayNgX4noKDaXivhVOp7bwGXq77MRzeL4-9qrRYKjuzHfZL7kNBCsqO185P0NI2Jtmw-EsqYsrCaHsfNRGRrTvUHUq3hWa859kK_5uNd7TeY2ZEwKVD8ezCmSfR59ZzyxTtuPpkCSHS9OtUvS3mqTYit73qcvprjl3R8hpjXLb8oftfpWr3hFRdpxrwuoQEO4QQ",
      "e": "AQAB",
      "x5c": [
        "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"
      ],
      "issuer": "https://login.microsoftonline.com/{tenantid}/v2.0"
    },
    {
      "kty": "RSA",
      "use": "sig",
      "kid": "1LTMzakihiRla_8z2BEJVXeWMqo",
      "x5t": "1LTMzakihiRla_8z2BEJVXeWMqo",
      "n": "3sKcJSD4cHwTY5jYm5lNEzqk3wON1CaARO5EoWIQt5u-X-ZnW61CiRZpWpfhKwRYU153td5R8p-AJDWT-NcEJ0MHU3KiuIEPmbgJpS7qkyURuHRucDM2lO4L4XfIlvizQrlyJnJcd09uLErZEO9PcvKiDHoois2B4fGj7CsAe5UZgExJvACDlsQSku2JUyDmZUZP2_u_gCuqNJM5o0hW7FKRI3MFoYCsqSEmHnnumuJ2jF0RHDRWQpodhlAR6uKLoiWHqHO3aG7scxYMj5cMzkpe1Kq_Dm5yyHkMCSJ_JaRhwymFfV_SWkqd3n-WVZT0ADLEq0RNi9tqZ43noUnO_w",
      "e": "AQAB",
      "x5c": [
        "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"
      ],
      "issuer": "https://login.microsoftonline.com/9188040d-6c67-4c5b-b112-36a304b66dad/v2.0"
    },
    {
      "kty": "RSA",
      "use": "sig",
      "kid": "xP_zn6I1YkXcUUmlBoPuXTGsaxk",
      "x5t": "xP_zn6I1YkXcUUmlBoPuXTGsaxk",
      "n": "2pWatafeb3mB0A73-Z-URwrubwDldWvivRu19GNC61MBOb3fZ4I4lyhUhNuS7aJRPJIFB6zl-HFx1nHpGg74BHe0z9skODHYZEACd2iKBIet55DdduIe1CXsZ9keyEmNaGv3XS4OW_7IDM0j5wR9OHugUifkH3PQIcFvTYanHmXojTmgjIOWoz7y0okpyN9-FbZRzdfx-ej-njaj5gR8r69muwO5wlTbIG20V40R6zYh-QODMUpayy7jDGFGw5vjFH9Ca0tLZcNQq__JKE_mp-0fODOAQobOrBUoASFkyCd95BVW7KJrndvW7ofRWaCTuZZOy5SnU4asbjMrgxFZFw",
      "e": "AQAB",
      "x5c": [
        "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"
      ],
      "issuer": "https://login.microsoftonline.com/9188040d-6c67-4c5b-b112-36a304b66dad/v2.0"
    }
  ]
}`

func LoadAzureKeys() ([]JwkRsaKey, error) {
	returnKeys := make([]JwkRsaKey, 0)
	sourceKeys := JwkKeys{}

	err := json.Unmarshal([]byte(SOURCE), &sourceKeys)
	if err != nil {
		return returnKeys, err
	}

	for _, k := range sourceKeys.Keys {
		fmt.Printf("kid = %q, e = %q, n = %q", k.KID, k.E, k.N)

		if k.Type == "RSA" {
			nb, err := base64.RawURLEncoding.DecodeString(k.N)
			if err != nil {
				return returnKeys, err
			}
			returnKeys = append(returnKeys, JwkRsaKey{
				KID: k.KID,
				PubKey: &rsa.PublicKey{
					N: new(big.Int).SetBytes(nb),
					E: 65537,
				},
			})
		}
	}

	for _, k := range returnKeys {
		fmt.Printf("kid = %q, key = %v\n", k.KID, k.PubKey)
	}

	return returnKeys, nil
}