Node.js – Azure AD JWT verification key runtime caching

/* 
declaring key into variable ahead allows us to write and cache it. 
Next time this function runs it sees, that key is not undefined, and just returns the existing object 
*/
var processedKey

async function getKey (kid) {

    if (!processedKey) {

        response = await axiosClient({url:process.env['jwks_uri']}).catch((error) => {
        return Promise.reject(error)
        })

        let keymatch = response.data?.keys.find((key) => {
            console.log(key.kid,'looking for',kid)
             return key.kid === kid 
         }) 
     
         processedKey = '-----BEGIN CERTIFICATE-----' +'\n' + keymatch.x5c + '\n' + '-----END CERTIFICATE-----'
     
         if (!keymatch) {return Promise.reject('no matching key')}
    }
   
    return processedKey
}

module.exports = {
    jwtverify,getKey
}